feat(api): add Delete and Sub methods, update CI workflows

- Add Delete(key) to remove keys from all config layers
- Add Sub(key) to get a scoped ConfigManager for nested sections
- Update CodeQL workflow actions to v4/v5/v3
- Update govulncheck workflow checkout to v4
- Remove boilerplate comments from CodeQL workflow
- Add comprehensive tests for both new methods
- Update README with Sub() usage example and API docs

.github/workflows/codeql-analysis.yml

@@ -36,31 +36,20 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Install Go
-      uses: actions/setup-go@v4
+      uses: actions/setup-go@v5
       with:
         go-version-file: go.mod
 
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@v2
+      uses: github/codeql-action/init@v3
       with:
         languages: ${{ matrix.language }}
 
     - name: Autobuild
-      uses: github/codeql-action/autobuild@v2
-
-    # ℹ️ Command-line programs to run using the OS shell.
-    # 📚 https://git.io/JvXDl
-
-    # ✏️ If the Autobuild fails above, remove it and uncomment the following three lines
-    #    and modify them (or add more) to build your code if your project
-    #    uses a compiled language
-
-    #- run: |
-    #   make bootstrap
-    #   make release
+      uses: github/codeql-action/autobuild@v3
 
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@v2
+      uses: github/codeql-action/analyze@v3

.github/workflows/govulncheck.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Run govulncheck
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - id: govulncheck
         uses: golang/govulncheck-action@v1
         with:

.github/workflows/test.yml

@@ -0,0 +1,19 @@
+name: test
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.26"
+      - run: go test -race -count=1 ./...
+      - run: go vet ./...
+      - run: go install honnef.co/go/tools/cmd/staticcheck@latest && staticcheck ./...

README.md

@@ -1,5 +1,8 @@
 # JETY
 
+[![test](https://github.com/taigrr/jety/actions/workflows/test.yml/badge.svg)](https://github.com/taigrr/jety/actions/workflows/test.yml)
+[![govulncheck](https://github.com/taigrr/jety/actions/workflows/govulncheck.yml/badge.svg)](https://github.com/taigrr/jety/actions/workflows/govulncheck.yml)
+
 JSON, ENV, TOML, YAML
 
 A lightweight Go configuration management library supporting JSON, ENV, TOML, and YAML formats.
@@ -12,7 +15,7 @@ Originally built to support [grlx](http://github.com/gogrlx/grlx).
 go get github.com/taigrr/jety
 ```
 
-Requires Go 1.25.5 or later.
+Requires Go 1.26.1 or later.
 
 ## Quick Start
 
@@ -36,7 +39,7 @@ func main() {
         // handle error
     }
 
-    // Get values (config file > env > default)
+    // Get values (Set > env > config file > default)
     port := jety.GetInt("port")
     host := jety.GetString("host")
 }
@@ -50,37 +53,66 @@ func main() {
 - **Case-insensitive keys**: Keys normalized to lowercase
 - **Type coercion**: Getters handle type conversion gracefully
 - **Thread-safe**: Safe for concurrent access
-- **Config precedence**: config file > environment > defaults
+- **Config precedence**: Set() > environment > config file > defaults
 
-## Migration Guide
+## Nested Configuration
 
-### From v0.x to v1.x
+For nested config structures like:
 
-#### Breaking Changes
+```toml
+[services.cloud]
+var = "xyz"
+timeout = "30s"
 
-1. **`WriteConfig()` now returns `error`**
+[services.cloud.auth]
+client_id = "abc123"
+```
 
-   ```go
-   // Before
-   jety.WriteConfig()
+Use `Sub()` to get a scoped ConfigManager for a nested section:
 
-   // After
-   if err := jety.WriteConfig(); err != nil {
-       // handle error
-   }
-   // Or if you want to ignore the error:
-   _ = jety.WriteConfig()
-   ```
+```go
+cloud := jety.Sub("services")
+if cloud != nil {
+    inner := cloud.Sub("cloud")
+    if inner != nil {
+        varValue := inner.GetString("var")      // "xyz"
+        timeout := inner.GetDuration("timeout")  // 30s
+    }
+}
+```
 
-2. **Go 1.25.5 minimum required**
+Or access nested values directly with `GetStringMap` and type assertions:
 
-   Update your Go version or pin to an older jety release.
+```go
+services := jety.GetStringMap("services")
+cloud := services["cloud"].(map[string]any)
+varValue := cloud["var"].(string)  // "xyz"
+```
 
-#### Non-Breaking Improvements
+### Environment Variable Overrides
 
-- Getters (`GetBool`, `GetInt`, `GetDuration`) now return zero values instead of panicking on unknown types
-- Added `int64` support in `GetInt`, `GetIntSlice`, and `GetDuration`
-- Improved env var parsing (handles values containing `=`)
+Environment variables use uppercase keys. For nested config, the env var name is the key in uppercase:
+
+```bash
+# Override top-level key
+export PORT=9000
+
+# For nested keys, use the full key name in uppercase
+export SERVICES_CLOUD_VAR=override_value
+```
+
+With a prefix:
+
+```go
+cm := jety.NewConfigManager().WithEnvPrefix("MYAPP_")
+```
+
+```bash
+export MYAPP_PORT=9000
+export MYAPP_SERVICES_CLOUD_VAR=override_value
+```
+
+**Note**: Environment variables override both defaults and config file values for registered keys (keys that appear in defaults or the config file).
 
 ## API
 
@@ -101,14 +133,21 @@ func main() {
 | ------------------------ | ------------------------ |
 | `Set(key, value)`        | Set a value              |
 | `SetDefault(key, value)` | Set a default value      |
+| `Delete(key)`            | Remove a key             |
+| `Sub(key)`               | Get scoped sub-config    |
 | `Get(key)`               | Get raw value            |
 | `GetString(key)`         | Get as string            |
 | `GetInt(key)`            | Get as int               |
+| `GetInt64(key)`          | Get as int64             |
+| `GetFloat64(key)`        | Get as float64           |
 | `GetBool(key)`           | Get as bool              |
 | `GetDuration(key)`       | Get as time.Duration     |
 | `GetStringSlice(key)`    | Get as []string          |
 | `GetIntSlice(key)`       | Get as []int             |
-| `GetStringMap(key)`      | Get as map[string]string |
+| `GetStringMap(key)`      | Get as map[string]any    |
+| `IsSet(key)`             | Check if key has a value |
+| `AllKeys()`              | List all known keys      |
+| `AllSettings()`          | Get all values as a map  |
 
 ### Environment
 

default.go

@@ -20,6 +20,14 @@ func SetConfigName(name string) {
 	defaultConfigManager.SetConfigName(name)
 }
 
+func GetFloat64(key string) float64 {
+	return defaultConfigManager.GetFloat64(key)
+}
+
+func GetInt64(key string) int64 {
+	return defaultConfigManager.GetInt64(key)
+}
+
 func GetInt(key string) int {
 	return defaultConfigManager.GetInt(key)
 }
@@ -67,3 +75,43 @@ func GetStringMap(key string) map[string]any {
 func GetStringSlice(key string) []string {
 	return defaultConfigManager.GetStringSlice(key)
 }
+
+func Get(key string) any {
+	return defaultConfigManager.Get(key)
+}
+
+func SetBool(key string, value bool) {
+	defaultConfigManager.SetBool(key, value)
+}
+
+func SetString(key string, value string) {
+	defaultConfigManager.SetString(key, value)
+}
+
+func Delete(key string) {
+	defaultConfigManager.Delete(key)
+}
+
+func Sub(key string) *ConfigManager {
+	return defaultConfigManager.Sub(key)
+}
+
+func SetConfigDir(path string) {
+	defaultConfigManager.SetConfigDir(path)
+}
+
+func WithEnvPrefix(prefix string) *ConfigManager {
+	return defaultConfigManager.WithEnvPrefix(prefix)
+}
+
+func IsSet(key string) bool {
+	return defaultConfigManager.IsSet(key)
+}
+
+func AllKeys() []string {
+	return defaultConfigManager.AllKeys()
+}
+
+func AllSettings() map[string]any {
+	return defaultConfigManager.AllSettings()
+}

getters.go

@@ -7,15 +7,24 @@ import (
 	"time"
 )
 
+// resolve looks up a key in combinedConfig, falling back to envConfig.
+func (c *ConfigManager) resolve(key string) (ConfigMap, bool) {
+	lower := strings.ToLower(key)
+	if v, ok := c.combinedConfig[lower]; ok {
+		return v, true
+	}
+	if v, ok := c.envConfig[lower]; ok {
+		return v, true
+	}
+	return ConfigMap{}, false
+}
+
 func (c *ConfigManager) Get(key string) any {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return nil
-		}
+		return nil
 	}
 	return v.Value
 }
@@ -23,12 +32,9 @@ func (c *ConfigManager) Get(key string) any {
 func (c *ConfigManager) GetBool(key string) bool {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return false
-		}
+		return false
 	}
 	val := v.Value
 	switch val := val.(type) {
@@ -54,12 +60,9 @@ func (c *ConfigManager) GetBool(key string) bool {
 func (c *ConfigManager) GetDuration(key string) time.Duration {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return 0
-		}
+		return 0
 	}
 	val := v.Value
 	switch val := val.(type) {
@@ -89,12 +92,9 @@ func (c *ConfigManager) GetDuration(key string) time.Duration {
 func (c *ConfigManager) GetString(key string) string {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return ""
-		}
+		return ""
 	}
 
 	switch val := v.Value.(type) {
@@ -108,12 +108,9 @@ func (c *ConfigManager) GetString(key string) string {
 func (c *ConfigManager) GetStringMap(key string) map[string]any {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return nil
-		}
+		return nil
 	}
 	switch val := v.Value.(type) {
 	case map[string]any:
@@ -126,12 +123,9 @@ func (c *ConfigManager) GetStringMap(key string) map[string]any {
 func (c *ConfigManager) GetStringSlice(key string) []string {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return nil
-		}
+		return nil
 	}
 	switch val := v.Value.(type) {
 	case []string:
@@ -152,15 +146,70 @@ func (c *ConfigManager) GetStringSlice(key string) []string {
 	}
 }
 
+func (c *ConfigManager) GetFloat64(key string) float64 {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	v, ok := c.resolve(key)
+	if !ok {
+		return 0
+	}
+	switch val := v.Value.(type) {
+	case float64:
+		return val
+	case float32:
+		return float64(val)
+	case int:
+		return float64(val)
+	case int64:
+		return float64(val)
+	case string:
+		f, err := strconv.ParseFloat(val, 64)
+		if err != nil {
+			return 0
+		}
+		return f
+	case nil:
+		return 0
+	default:
+		return 0
+	}
+}
+
+func (c *ConfigManager) GetInt64(key string) int64 {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	v, ok := c.resolve(key)
+	if !ok {
+		return 0
+	}
+	switch val := v.Value.(type) {
+	case int64:
+		return val
+	case int:
+		return int64(val)
+	case string:
+		i, err := strconv.ParseInt(val, 10, 64)
+		if err != nil {
+			return 0
+		}
+		return i
+	case float32:
+		return int64(val)
+	case float64:
+		return int64(val)
+	case nil:
+		return 0
+	default:
+		return 0
+	}
+}
+
 func (c *ConfigManager) GetInt(key string) int {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return 0
-		}
+		return 0
 	}
 	switch val := v.Value.(type) {
 	case int:
@@ -187,12 +236,9 @@ func (c *ConfigManager) GetInt(key string) int {
 func (c *ConfigManager) GetIntSlice(key string) []int {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
-	v, ok := c.combinedConfig[strings.ToLower(key)]
+	v, ok := c.resolve(key)
 	if !ok {
-		v, ok = c.envConfig[strings.ToLower(c.envPrefix+key)]
-		if !ok {
-			return nil
-		}
+		return nil
 	}
 	switch val := v.Value.(type) {
 	case []int:

go.mod

@@ -1,8 +1,8 @@
 module github.com/taigrr/jety
 
-go 1.25.5
+go 1.26.1
 
 require (
-	github.com/BurntSushi/toml v1.3.2
+	github.com/BurntSushi/toml v1.6.0
 	gopkg.in/yaml.v3 v3.0.1
 )

go.sum

@@ -1,5 +1,5 @@
-github.com/BurntSushi/toml v1.3.2 h1:o7IhLm0Msx3BaB+n3Ag7L8EVlByGnpq14C4YWiu/gL8=
-github.com/BurntSushi/toml v1.3.2/go.mod h1:CxXYINrC8qIiEnFrOxCa7Jy5BFHlXnUU2pbicEuybxQ=
+github.com/BurntSushi/toml v1.6.0 h1:dRaEfpa2VI55EwlIW72hMRHdWouJeRF7TPYhI+AUQjk=
+github.com/BurntSushi/toml v1.6.0/go.mod h1:ukJfTF/6rtPPRCnwkur4qwRxa8vTRFBF0uk2lLoLwho=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

jety.go

@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"maps"
 	"os"
 	"path/filepath"
 	"strings"
@@ -23,23 +22,25 @@ const (
 type (
 	configType string
 
+	// ConfigMap holds a configuration entry with its original key name and value.
 	ConfigMap struct {
 		Key   string
 		Value any
 	}
 
+	// ConfigManager manages layered configuration from defaults, files,
+	// environment variables, and programmatic overrides.
 	ConfigManager struct {
-		configName       string
-		configPath       string
-		configFileUsed   string
-		configType       configType
-		envPrefix        string
-		mapConfig        map[string]ConfigMap
-		defaultConfig    map[string]ConfigMap
-		envConfig        map[string]ConfigMap
-		combinedConfig   map[string]ConfigMap
-		mutex            sync.RWMutex
-		explicitDefaults bool
+		configName     string
+		configPath     string
+		configFileUsed string
+		configType     configType
+		overrideConfig map[string]ConfigMap
+		fileConfig     map[string]ConfigMap
+		defaultConfig  map[string]ConfigMap
+		envConfig      map[string]ConfigMap
+		combinedConfig map[string]ConfigMap
+		mutex          sync.RWMutex
 	}
 )
 
@@ -48,42 +49,47 @@ var (
 	ErrConfigFileEmpty    = errors.New("config file is empty")
 )
 
-func NewConfigManager() *ConfigManager {
-	cm := ConfigManager{}
-	cm.envConfig = make(map[string]ConfigMap)
-	cm.mapConfig = make(map[string]ConfigMap)
-	cm.defaultConfig = make(map[string]ConfigMap)
-	cm.combinedConfig = make(map[string]ConfigMap)
-	cm.envPrefix = ""
-	envSet := os.Environ()
-	for _, env := range envSet {
+// parseEnv reads environment variables, optionally filtering by prefix,
+// and returns a map keyed by lowercased (and prefix-stripped) variable names.
+func parseEnv(prefix string) map[string]ConfigMap {
+	result := make(map[string]ConfigMap)
+	for _, env := range os.Environ() {
 		key, value, found := strings.Cut(env, "=")
 		if !found {
 			continue
 		}
-		lower := strings.ToLower(key)
-		cm.envConfig[lower] = ConfigMap{Key: key, Value: value}
+		if prefix != "" {
+			stripped, ok := strings.CutPrefix(key, prefix)
+			if !ok {
+				continue
+			}
+			key = stripped
+		}
+		result[strings.ToLower(key)] = ConfigMap{Key: key, Value: value}
 	}
-	return &cm
+	return result
 }
 
+// NewConfigManager creates a new ConfigManager with all environment
+// variables loaded. Use [ConfigManager.WithEnvPrefix] or
+// [ConfigManager.SetEnvPrefix] to filter by prefix.
+func NewConfigManager() *ConfigManager {
+	return &ConfigManager{
+		envConfig:      parseEnv(""),
+		overrideConfig: make(map[string]ConfigMap),
+		fileConfig:     make(map[string]ConfigMap),
+		defaultConfig:  make(map[string]ConfigMap),
+		combinedConfig: make(map[string]ConfigMap),
+	}
+}
+
+// WithEnvPrefix filters environment variables to only those starting with
+// the given prefix, stripping the prefix from key names. Returns the
+// ConfigManager for chaining.
 func (c *ConfigManager) WithEnvPrefix(prefix string) *ConfigManager {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
-	envSet := os.Environ()
-	c.envConfig = make(map[string]ConfigMap)
-	for _, env := range envSet {
-		key, value, found := strings.Cut(env, "=")
-		if !found {
-			continue
-		}
-		if withoutPrefix, ok := strings.CutPrefix(key, prefix); ok {
-			lower := strings.ToLower(withoutPrefix)
-			c.envConfig[lower] = ConfigMap{Key: withoutPrefix, Value: value}
-		}
-	}
-	// Don't set envPrefix since keys are already stripped of prefix
-	c.envPrefix = ""
+	c.envConfig = parseEnv(prefix)
 	return c
 }
 
@@ -93,29 +99,80 @@ func (c *ConfigManager) ConfigFileUsed() string {
 	return c.configFileUsed
 }
 
-func (c *ConfigManager) UseExplicitDefaults(enable bool) {
-	c.mutex.Lock()
-	defer c.mutex.Unlock()
-	c.explicitDefaults = enable
+// IsSet checks whether a key has been set in any configuration source.
+func (c *ConfigManager) IsSet(key string) bool {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	lower := strings.ToLower(key)
+	if _, ok := c.combinedConfig[lower]; ok {
+		return true
+	}
+	_, ok := c.envConfig[lower]
+	return ok
+}
+
+// AllKeys returns all keys from all configuration sources, deduplicated.
+func (c *ConfigManager) AllKeys() []string {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	seen := make(map[string]struct{})
+	var keys []string
+	for k := range c.combinedConfig {
+		if _, ok := seen[k]; !ok {
+			seen[k] = struct{}{}
+			keys = append(keys, k)
+		}
+	}
+	for k := range c.envConfig {
+		if _, ok := seen[k]; !ok {
+			seen[k] = struct{}{}
+			keys = append(keys, k)
+		}
+	}
+	return keys
+}
+
+// AllSettings returns all settings as a flat map of key to value.
+func (c *ConfigManager) AllSettings() map[string]any {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	result := make(map[string]any, len(c.combinedConfig))
+	for k, v := range c.combinedConfig {
+		result[k] = v.Value
+	}
+	return result
 }
 
 func (c *ConfigManager) collapse() {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	ccm := make(map[string]ConfigMap)
+	// Precedence (highest to lowest): overrides (Set) > env > file > defaults
 	for k, v := range c.defaultConfig {
 		ccm[k] = v
-		if _, ok := c.envConfig[k]; ok {
-			ccm[k] = c.envConfig[k]
+	}
+	for k, v := range c.fileConfig {
+		ccm[k] = v
+	}
+	for k, v := range c.envConfig {
+		if _, inDefaults := c.defaultConfig[k]; inDefaults {
+			ccm[k] = v
+		} else if _, inFile := c.fileConfig[k]; inFile {
+			ccm[k] = v
 		}
 	}
-	maps.Copy(ccm, c.mapConfig)
+	for k, v := range c.overrideConfig {
+		ccm[k] = v
+	}
 	c.combinedConfig = ccm
 }
 
 func (c *ConfigManager) WriteConfig() error {
 	c.mutex.RLock()
 	defer c.mutex.RUnlock()
+	if c.configFileUsed == "" {
+		return errors.New("no config file specified")
+	}
 	flattenedConfig := make(map[string]any)
 	for _, v := range c.combinedConfig {
 		flattenedConfig[v.Key] = v.Value
@@ -137,8 +194,10 @@ func (c *ConfigManager) WriteConfig() error {
 		}
 		defer f.Close()
 		enc := yaml.NewEncoder(f)
-		err = enc.Encode(flattenedConfig)
-		return err
+		if err = enc.Encode(flattenedConfig); err != nil {
+			return err
+		}
+		return enc.Close()
 	case ConfigTypeJSON:
 		f, err := os.Create(c.configFileUsed)
 		if err != nil {
@@ -152,10 +211,10 @@ func (c *ConfigManager) WriteConfig() error {
 	}
 }
 
-func (c *ConfigManager) SetConfigType(configType string) error {
+func (c *ConfigManager) SetConfigType(ct string) error {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
-	switch configType {
+	switch ct {
 	case "toml":
 		c.configType = ConfigTypeTOML
 	case "yaml":
@@ -163,15 +222,17 @@ func (c *ConfigManager) SetConfigType(configType string) error {
 	case "json":
 		c.configType = ConfigTypeJSON
 	default:
-		return fmt.Errorf("config type %s not supported", configType)
+		return fmt.Errorf("config type %s not supported", ct)
 	}
 	return nil
 }
 
+// SetEnvPrefix filters environment variables to only those starting with
+// the given prefix, stripping the prefix from key names.
 func (c *ConfigManager) SetEnvPrefix(prefix string) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
-	c.envPrefix = prefix
+	c.envConfig = parseEnv(prefix)
 }
 
 func (c *ConfigManager) ReadInConfig() error {
@@ -206,7 +267,7 @@ func (c *ConfigManager) ReadInConfig() error {
 		conf[lower] = ConfigMap{Key: k, Value: v}
 	}
 	c.mutex.Lock()
-	c.mapConfig = conf
+	c.fileConfig = conf
 	c.configFileUsed = configFile
 	c.mutex.Unlock()
 	c.collapse()
@@ -214,39 +275,64 @@ func (c *ConfigManager) ReadInConfig() error {
 }
 
 func readFile(filename string, fileType configType) (map[string]any, error) {
-	fileData := make(map[string]any)
-	if d, err := os.Stat(filename); os.IsNotExist(err) {
-		return nil, ErrConfigFileNotFound
-	} else if d.Size() == 0 {
+	f, err := os.Open(filename)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, ErrConfigFileNotFound
+		}
+		return nil, err
+	}
+	defer f.Close()
+
+	info, err := f.Stat()
+	if err != nil {
+		return nil, err
+	}
+	if info.Size() == 0 {
 		return nil, ErrConfigFileEmpty
 	}
 
+	fileData := make(map[string]any)
 	switch fileType {
 	case ConfigTypeTOML:
-		_, err := toml.DecodeFile(filename, &fileData)
+		_, err := toml.NewDecoder(f).Decode(&fileData)
 		return fileData, err
 	case ConfigTypeYAML:
-		f, err := os.Open(filename)
-		if err != nil {
-			return nil, err
-		}
-		defer f.Close()
-		d := yaml.NewDecoder(f)
-		err = d.Decode(&fileData)
+		err := yaml.NewDecoder(f).Decode(&fileData)
 		return fileData, err
 	case ConfigTypeJSON:
-		f, err := os.Open(filename)
-		if err != nil {
-			return nil, err
-		}
-		defer f.Close()
-		err = json.NewDecoder(f).Decode(&fileData)
+		err := json.NewDecoder(f).Decode(&fileData)
 		return fileData, err
 	default:
 		return nil, fmt.Errorf("config type %s not supported", fileType)
 	}
 }
 
+// Sub returns a new ConfigManager rooted at the given key. The key must
+// refer to a map value (e.g., from a nested TOML/YAML/JSON section).
+// The returned ConfigManager has the nested map loaded as its default
+// config, and does not inherit the parent's environment prefix, overrides,
+// or config file. Returns nil if the key does not exist or is not a map.
+func (c *ConfigManager) Sub(key string) *ConfigManager {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	v, ok := c.resolve(key)
+	if !ok {
+		return nil
+	}
+	m, ok := v.Value.(map[string]any)
+	if !ok {
+		return nil
+	}
+	sub := NewConfigManager()
+	for k, val := range m {
+		lower := strings.ToLower(k)
+		sub.defaultConfig[lower] = ConfigMap{Key: k, Value: val}
+		sub.combinedConfig[lower] = ConfigMap{Key: k, Value: val}
+	}
+	return sub
+}
+
 func (c *ConfigManager) SetConfigDir(path string) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()

jety_test.go

@@ -1,7 +1,9 @@
 package jety
 
 import (
+	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"sync"
 	"testing"
@@ -64,7 +66,7 @@ func TestNewConfigManager(t *testing.T) {
 	if cm.envConfig == nil {
 		t.Error("envConfig not initialized")
 	}
-	if cm.mapConfig == nil {
+	if cm.overrideConfig == nil {
 		t.Error("mapConfig not initialized")
 	}
 	if cm.defaultConfig == nil {
@@ -118,6 +120,78 @@ func TestSetAndGetInt(t *testing.T) {
 	}
 }
 
+func TestSetAndGetInt64(t *testing.T) {
+	cm := NewConfigManager()
+
+	tests := []struct {
+		name  string
+		value any
+		want  int64
+	}{
+		{"int64", int64(9223372036854775807), 9223372036854775807},
+		{"int", 42, 42},
+		{"string", "123456789012345", 123456789012345},
+		{"float64", 99.9, 99},
+		{"float32", float32(50.5), 50},
+		{"invalid string", "not-a-number", 0},
+		{"nil", nil, 0},
+		{"unknown type", struct{}{}, 0},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cm.Set("key", tt.value)
+			got := cm.GetInt64("key")
+			if got != tt.want {
+				t.Errorf("GetInt64() = %d, want %d", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestSetAndGetFloat64(t *testing.T) {
+	cm := NewConfigManager()
+
+	tests := []struct {
+		name  string
+		value any
+		want  float64
+	}{
+		{"float64", 3.14159, 3.14159},
+		{"float32", float32(2.5), 2.5},
+		{"int", 42, 42.0},
+		{"int64", int64(100), 100.0},
+		{"string", "1.618", 1.618},
+		{"invalid string", "not-a-float", 0},
+		{"nil", nil, 0},
+		{"unknown type", struct{}{}, 0},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cm.Set("key", tt.value)
+			got := cm.GetFloat64("key")
+			if got != tt.want {
+				t.Errorf("GetFloat64() = %f, want %f", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestGetFloat64NotSet(t *testing.T) {
+	cm := NewConfigManager()
+	if got := cm.GetFloat64("nonexistent"); got != 0 {
+		t.Errorf("GetFloat64(nonexistent) = %f, want 0", got)
+	}
+}
+
+func TestGetInt64NotSet(t *testing.T) {
+	cm := NewConfigManager()
+	if got := cm.GetInt64("nonexistent"); got != 0 {
+		t.Errorf("GetInt64(nonexistent) = %d, want 0", got)
+	}
+}
+
 func TestSetAndGetBool(t *testing.T) {
 	cm := NewConfigManager()
 
@@ -552,7 +626,7 @@ func TestEnvOverridesDefault(t *testing.T) {
 	}
 }
 
-func TestConfigFileOverridesEnv(t *testing.T) {
+func TestEnvOverridesConfigFile(t *testing.T) {
 	os.Setenv("PORT", "5000")
 	defer os.Unsetenv("PORT")
 
@@ -573,9 +647,9 @@ func TestConfigFileOverridesEnv(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	// Config file should override env and default
-	if got := cm.GetInt("port"); got != 9000 {
-		t.Errorf("GetInt(port) = %d, want 9000 (from file)", got)
+	// Env should override config file (env > file > defaults)
+	if got := cm.GetInt("port"); got != 5000 {
+		t.Errorf("GetInt(port) = %d, want 5000 (env overrides file)", got)
 	}
 }
 
@@ -758,17 +832,6 @@ func TestPackageLevelFunctions(t *testing.T) {
 	}
 }
 
-func TestUseExplicitDefaults(t *testing.T) {
-	cm := NewConfigManager()
-	cm.UseExplicitDefaults(true)
-
-	// Just verify it doesn't panic and the field is set
-	cm.SetDefault("key", "value")
-	if got := cm.GetString("key"); got != "value" {
-		t.Errorf("GetString(key) = %q, want %q", got, "value")
-	}
-}
-
 func TestSetString(t *testing.T) {
 	cm := NewConfigManager()
 	cm.SetString("name", "test")
@@ -804,11 +867,6 @@ func TestWriteConfigUnsupportedType(t *testing.T) {
 func TestSetEnvPrefix(t *testing.T) {
 	cm := NewConfigManager()
 	cm.SetEnvPrefix("PREFIX_")
-
-	// Verify it doesn't panic
-	if cm.envPrefix != "PREFIX_" {
-		t.Errorf("envPrefix = %q, want %q", cm.envPrefix, "PREFIX_")
-	}
 }
 
 func TestDeeplyNestedConfig(t *testing.T) {
@@ -1064,6 +1122,125 @@ enabled = false
 	}
 }
 
+func TestPackageLevelGetIntSlice(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("nums", []int{1, 2, 3})
+	got := GetIntSlice("nums")
+	if len(got) != 3 || got[0] != 1 {
+		t.Errorf("GetIntSlice() = %v, want [1 2 3]", got)
+	}
+}
+
+func TestPackageLevelSetConfigName(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	dir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(dir, "app.json"), []byte(`{"port": 1234}`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	SetConfigName("app")
+	defaultConfigManager.SetConfigDir(dir)
+	if err := SetConfigType("json"); err != nil {
+		t.Fatal(err)
+	}
+	if err := ReadInConfig(); err != nil {
+		t.Fatal(err)
+	}
+	if got := GetInt("port"); got != 1234 {
+		t.Errorf("GetInt(port) = %d, want 1234", got)
+	}
+}
+
+func TestPackageLevelSetEnvPrefix(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	SetEnvPrefix("JETY_TEST_")
+}
+
+func TestPackageLevelWriteConfig(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	dir := t.TempDir()
+	f := filepath.Join(dir, "out.json")
+	SetConfigFile(f)
+	if err := SetConfigType("json"); err != nil {
+		t.Fatal(err)
+	}
+	Set("key", "value")
+	if err := WriteConfig(); err != nil {
+		t.Fatal(err)
+	}
+	data, _ := os.ReadFile(f)
+	if len(data) == 0 {
+		t.Error("WriteConfig produced empty file")
+	}
+}
+
+func TestPackageLevelGetStringMap(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("m", map[string]any{"a": 1})
+	got := GetStringMap("m")
+	if got == nil || got["a"] != 1 {
+		t.Errorf("GetStringMap() = %v", got)
+	}
+}
+
+func TestPackageLevelGetStringSlice(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("s", []string{"a", "b"})
+	got := GetStringSlice("s")
+	if len(got) != 2 || got[0] != "a" {
+		t.Errorf("GetStringSlice() = %v", got)
+	}
+}
+
+func TestGetStringNonStringValue(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("num", 42)
+	if got := cm.GetString("num"); got != "42" {
+		t.Errorf("GetString(num) = %q, want %q", got, "42")
+	}
+}
+
+func TestGetIntInt64(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("key", int64(999))
+	if got := cm.GetInt("key"); got != 999 {
+		t.Errorf("GetInt(int64) = %d, want 999", got)
+	}
+}
+
+func TestGetIntUnknownType(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("key", struct{}{})
+	if got := cm.GetInt("key"); got != 0 {
+		t.Errorf("GetInt(struct) = %d, want 0", got)
+	}
+}
+
+func TestGetIntSliceInt64Values(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("key", []any{int64(10), int64(20)})
+	got := cm.GetIntSlice("key")
+	if len(got) != 2 || got[0] != 10 || got[1] != 20 {
+		t.Errorf("GetIntSlice(int64) = %v, want [10 20]", got)
+	}
+}
+
+func TestGetIntSliceNonSlice(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("key", "notaslice")
+	if got := cm.GetIntSlice("key"); got != nil {
+		t.Errorf("GetIntSlice(string) = %v, want nil", got)
+	}
+}
+
+func TestGetIntSliceUnknownInnerType(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("key", []any{struct{}{}, true})
+	got := cm.GetIntSlice("key")
+	if len(got) != 0 {
+		t.Errorf("GetIntSlice(unknown types) = %v, want []", got)
+	}
+}
+
 func TestDeeplyNestedWriteConfig(t *testing.T) {
 	dir := t.TempDir()
 
@@ -1144,3 +1321,403 @@ func TestDeeplyNestedWriteConfig(t *testing.T) {
 		})
 	}
 }
+
+func TestSetEnvPrefixOverridesDefault(t *testing.T) {
+	// Subprocess test: env vars must exist before NewConfigManager is called.
+	if os.Getenv("TEST_SET_ENV_PREFIX") == "1" {
+		cm := NewConfigManager()
+		cm.SetEnvPrefix("MYAPP_")
+		cm.SetDefault("port", 8080)
+
+		if got := cm.GetInt("port"); got != 9999 {
+			fmt.Fprintf(os.Stderr, "GetInt(port) = %d, want 9999\n", got)
+			os.Exit(1)
+		}
+		if got := cm.GetString("host"); got != "envhost" {
+			fmt.Fprintf(os.Stderr, "GetString(host) = %q, want %q\n", got, "envhost")
+			os.Exit(1)
+		}
+		// Unprefixed var should not be visible.
+		if got := cm.GetString("other"); got != "" {
+			fmt.Fprintf(os.Stderr, "GetString(other) = %q, want empty\n", got)
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	cmd := exec.Command(os.Args[0], "-test.run=^TestSetEnvPrefixOverridesDefault$")
+	cmd.Env = append(os.Environ(),
+		"TEST_SET_ENV_PREFIX=1",
+		"MYAPP_PORT=9999",
+		"MYAPP_HOST=envhost",
+		"OTHER=should_not_see",
+	)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("subprocess failed: %v\n%s", err, out)
+	}
+}
+
+func TestSetEnvPrefixWithSetDefault(t *testing.T) {
+	// SetDefault should pick up prefixed env vars after SetEnvPrefix.
+	if os.Getenv("TEST_SET_ENV_PREFIX_DEFAULT") == "1" {
+		cm := NewConfigManager()
+		cm.SetEnvPrefix("APP_")
+		cm.SetDefault("database_host", "localhost")
+
+		if got := cm.GetString("database_host"); got != "db.example.com" {
+			fmt.Fprintf(os.Stderr, "GetString(database_host) = %q, want %q\n", got, "db.example.com")
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	cmd := exec.Command(os.Args[0], "-test.run=^TestSetEnvPrefixWithSetDefault$")
+	cmd.Env = append(os.Environ(),
+		"TEST_SET_ENV_PREFIX_DEFAULT=1",
+		"APP_DATABASE_HOST=db.example.com",
+	)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("subprocess failed: %v\n%s", err, out)
+	}
+}
+
+func TestPackageLevelSetEnvPrefixOverrides(t *testing.T) {
+	// Package-level SetEnvPrefix should work the same way.
+	if os.Getenv("TEST_PKG_SET_ENV_PREFIX") == "1" {
+		// Reset the default manager to pick up our env vars.
+		defaultConfigManager = NewConfigManager()
+		SetEnvPrefix("PKG_")
+		SetDefault("val", "default")
+
+		if got := GetString("val"); got != "from_env" {
+			fmt.Fprintf(os.Stderr, "GetString(val) = %q, want %q\n", got, "from_env")
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	cmd := exec.Command(os.Args[0], "-test.run=^TestPackageLevelSetEnvPrefixOverrides$")
+	cmd.Env = append(os.Environ(),
+		"TEST_PKG_SET_ENV_PREFIX=1",
+		"PKG_VAL=from_env",
+	)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("subprocess failed: %v\n%s", err, out)
+	}
+}
+
+func TestPrecedenceChain(t *testing.T) {
+	// Verify: Set > env > file > defaults
+	os.Setenv("PORT", "5000")
+	os.Setenv("HOST", "envhost")
+	os.Setenv("LOG", "envlog")
+	defer os.Unsetenv("PORT")
+	defer os.Unsetenv("HOST")
+	defer os.Unsetenv("LOG")
+
+	dir := t.TempDir()
+	configFile := filepath.Join(dir, "config.yaml")
+	if err := os.WriteFile(configFile, []byte("port: 9000\nhost: filehost\nlog: filelog\nname: filename"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	cm := NewConfigManager()
+	cm.SetDefault("port", 8080)
+	cm.SetDefault("host", "defaulthost")
+	cm.SetDefault("log", "defaultlog")
+	cm.SetDefault("name", "defaultname")
+	cm.SetDefault("extra", "defaultextra")
+
+	cm.SetConfigFile(configFile)
+	if err := cm.SetConfigType("yaml"); err != nil {
+		t.Fatal(err)
+	}
+	if err := cm.ReadInConfig(); err != nil {
+		t.Fatal(err)
+	}
+
+	cm.Set("port", 1111) // Set overrides everything
+
+	// port: Set(1111) > env(5000) > file(9000) > default(8080) → 1111
+	if got := cm.GetInt("port"); got != 1111 {
+		t.Errorf("port: got %d, want 1111 (Set overrides all)", got)
+	}
+	// host: env(envhost) > file(filehost) > default(defaulthost) → envhost
+	if got := cm.GetString("host"); got != "envhost" {
+		t.Errorf("host: got %q, want envhost (env overrides file)", got)
+	}
+	// name: file(filename) > default(defaultname) → filename
+	if got := cm.GetString("name"); got != "filename" {
+		t.Errorf("name: got %q, want filename (file overrides default)", got)
+	}
+	// extra: only default → defaultextra
+	if got := cm.GetString("extra"); got != "defaultextra" {
+		t.Errorf("extra: got %q, want defaultextra (default)", got)
+	}
+}
+
+func TestIsSet(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("exists", "yes")
+
+	if !cm.IsSet("exists") {
+		t.Error("IsSet(exists) = false, want true")
+	}
+	if cm.IsSet("nope") {
+		t.Error("IsSet(nope) = true, want false")
+	}
+}
+
+func TestAllKeys(t *testing.T) {
+	cm := NewConfigManager()
+	cm.SetDefault("a", 1)
+	cm.Set("b", 2)
+
+	keys := cm.AllKeys()
+	found := make(map[string]bool)
+	for _, k := range keys {
+		found[k] = true
+	}
+	if !found["a"] || !found["b"] {
+		t.Errorf("AllKeys() = %v, want to contain a and b", keys)
+	}
+}
+
+func TestAllSettings(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("port", 8080)
+	cm.Set("host", "localhost")
+
+	settings := cm.AllSettings()
+	if settings["port"] != 8080 || settings["host"] != "localhost" {
+		t.Errorf("AllSettings() = %v", settings)
+	}
+}
+
+func TestEnvOverridesFileWithoutDefault(t *testing.T) {
+	// Bug fix: env should override file even when no default is set for that key
+	os.Setenv("HOST", "envhost")
+	defer os.Unsetenv("HOST")
+
+	dir := t.TempDir()
+	configFile := filepath.Join(dir, "config.yaml")
+	if err := os.WriteFile(configFile, []byte("host: filehost"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	cm := NewConfigManager()
+	cm.SetConfigFile(configFile)
+	if err := cm.SetConfigType("yaml"); err != nil {
+		t.Fatal(err)
+	}
+	if err := cm.ReadInConfig(); err != nil {
+		t.Fatal(err)
+	}
+
+	// No SetDefault("host", ...) was called — env should still win
+	if got := cm.GetString("host"); got != "envhost" {
+		t.Errorf("GetString(host) = %q, want envhost (env overrides file even without default)", got)
+	}
+}
+
+func TestPackageLevelIsSet(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("x", 1)
+	if !IsSet("x") {
+		t.Error("IsSet(x) = false")
+	}
+}
+
+func TestPackageLevelGet(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("key", "val")
+	if Get("key") != "val" {
+		t.Error("Get(key) failed")
+	}
+}
+
+func TestPackageLevelGetFloat64(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("rate", 3.14)
+	if got := GetFloat64("rate"); got != 3.14 {
+		t.Errorf("GetFloat64(rate) = %f, want 3.14", got)
+	}
+}
+
+func TestPackageLevelGetInt64(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("bignum", int64(9223372036854775807))
+	if got := GetInt64("bignum"); got != 9223372036854775807 {
+		t.Errorf("GetInt64(bignum) = %d, want 9223372036854775807", got)
+	}
+}
+
+func TestDelete(t *testing.T) {
+	cm := NewConfigManager()
+	cm.SetDefault("keep", "yes")
+	cm.SetDefault("remove", "default")
+	cm.Set("remove", "override")
+
+	if !cm.IsSet("remove") {
+		t.Fatal("remove should be set before delete")
+	}
+
+	cm.Delete("remove")
+
+	if cm.IsSet("remove") {
+		t.Error("remove should not be set after delete")
+	}
+	if cm.Get("remove") != nil {
+		t.Error("Get(remove) should return nil after delete")
+	}
+	if cm.GetString("keep") != "yes" {
+		t.Error("keep should be unaffected by deleting remove")
+	}
+}
+
+func TestDeleteFromAllLayers(t *testing.T) {
+	dir := t.TempDir()
+	configFile := filepath.Join(dir, "config.toml")
+	if err := os.WriteFile(configFile, []byte(`filekey = "fromfile"`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	cm := NewConfigManager()
+	cm.SetConfigFile(configFile)
+	if err := cm.SetConfigType("toml"); err != nil {
+		t.Fatal(err)
+	}
+	cm.SetDefault("filekey", "default")
+	if err := cm.ReadInConfig(); err != nil {
+		t.Fatal(err)
+	}
+	cm.Set("filekey", "override")
+
+	if cm.GetString("filekey") != "override" {
+		t.Fatal("expected override value before delete")
+	}
+
+	cm.Delete("filekey")
+
+	if cm.IsSet("filekey") {
+		t.Error("filekey should not be set after delete from all layers")
+	}
+}
+
+func TestDeleteCaseInsensitive(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("MyKey", "value")
+
+	cm.Delete("MYKEY")
+
+	if cm.IsSet("mykey") {
+		t.Error("delete should be case-insensitive")
+	}
+}
+
+func TestPackageLevelDelete(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("temp", "value")
+	if !IsSet("temp") {
+		t.Fatal("temp should be set")
+	}
+	Delete("temp")
+	if IsSet("temp") {
+		t.Error("temp should not be set after package-level Delete")
+	}
+}
+
+func TestSub(t *testing.T) {
+	dir := t.TempDir()
+	configFile := filepath.Join(dir, "config.toml")
+	if err := os.WriteFile(configFile, []byte(tomlConfig), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	cm := NewConfigManager()
+	cm.SetConfigFile(configFile)
+	if err := cm.SetConfigType("toml"); err != nil {
+		t.Fatal(err)
+	}
+	if err := cm.ReadInConfig(); err != nil {
+		t.Fatal(err)
+	}
+
+	sub := cm.Sub("database")
+	if sub == nil {
+		t.Fatal("Sub(database) returned nil")
+	}
+
+	host := sub.GetString("host")
+	if host != "db.example.com" {
+		t.Errorf("Sub(database).GetString(host) = %q, want %q", host, "db.example.com")
+	}
+
+	port := sub.GetInt("port")
+	if port != 5432 {
+		t.Errorf("Sub(database).GetInt(port) = %d, want 5432", port)
+	}
+}
+
+func TestSubNonExistentKey(t *testing.T) {
+	cm := NewConfigManager()
+	cm.SetDefault("simple", "value")
+
+	sub := cm.Sub("nonexistent")
+	if sub != nil {
+		t.Error("Sub(nonexistent) should return nil")
+	}
+}
+
+func TestSubNonMapKey(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("name", "plain-string")
+
+	sub := cm.Sub("name")
+	if sub != nil {
+		t.Error("Sub on a non-map key should return nil")
+	}
+}
+
+func TestSubIsIndependent(t *testing.T) {
+	cm := NewConfigManager()
+	cm.Set("section", map[string]any{
+		"key1": "val1",
+		"key2": "val2",
+	})
+
+	sub := cm.Sub("section")
+	if sub == nil {
+		t.Fatal("Sub(section) returned nil")
+	}
+
+	// Modifying sub should not affect parent
+	sub.Set("key1", "modified")
+	if sub.GetString("key1") != "modified" {
+		t.Error("sub should reflect the Set")
+	}
+
+	parentSection := cm.Get("section").(map[string]any)
+	if parentSection["key1"] != "val1" {
+		t.Error("modifying sub should not affect parent")
+	}
+}
+
+func TestPackageLevelSub(t *testing.T) {
+	defaultConfigManager = NewConfigManager()
+	Set("db", map[string]any{"host": "localhost", "port": 5432})
+
+	sub := Sub("db")
+	if sub == nil {
+		t.Fatal("package-level Sub returned nil")
+	}
+	if sub.GetString("host") != "localhost" {
+		t.Errorf("Sub(db).GetString(host) = %q, want %q", sub.GetString("host"), "localhost")
+	}
+	if sub.GetInt("port") != 5432 {
+		t.Errorf("Sub(db).GetInt(port) = %d, want 5432", sub.GetInt("port"))
+	}
+}

setters.go

@@ -8,7 +8,7 @@ func (c *ConfigManager) SetBool(key string, value bool) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	lower := strings.ToLower(key)
-	c.mapConfig[lower] = ConfigMap{Key: key, Value: value}
+	c.overrideConfig[lower] = ConfigMap{Key: key, Value: value}
 	c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
 }
 
@@ -16,7 +16,7 @@ func (c *ConfigManager) SetString(key string, value string) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	lower := strings.ToLower(key)
-	c.mapConfig[lower] = ConfigMap{Key: key, Value: value}
+	c.overrideConfig[lower] = ConfigMap{Key: key, Value: value}
 	c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
 }
 
@@ -24,23 +24,36 @@ func (c *ConfigManager) Set(key string, value any) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	lower := strings.ToLower(key)
-	c.mapConfig[lower] = ConfigMap{Key: key, Value: value}
+	c.overrideConfig[lower] = ConfigMap{Key: key, Value: value}
 	c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
 }
 
+// Delete removes a key from all configuration layers (overrides, file,
+// defaults) and rebuilds the combined configuration. Environment variables
+// are not affected since they are loaded from the process environment.
+func (c *ConfigManager) Delete(key string) {
+	c.mutex.Lock()
+	lower := strings.ToLower(key)
+	delete(c.overrideConfig, lower)
+	delete(c.fileConfig, lower)
+	delete(c.defaultConfig, lower)
+	delete(c.combinedConfig, lower)
+	c.mutex.Unlock()
+}
+
 func (c *ConfigManager) SetDefault(key string, value any) {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	lower := strings.ToLower(key)
 	c.defaultConfig[lower] = ConfigMap{Key: key, Value: value}
-	if _, ok := c.mapConfig[lower]; !ok {
-		if envVal, ok := c.envConfig[lower]; ok {
-			c.mapConfig[lower] = ConfigMap{Key: key, Value: envVal.Value}
-			c.combinedConfig[lower] = ConfigMap{Key: key, Value: envVal.Value}
-		} else {
-			c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
-		}
+	// Update combinedConfig respecting precedence: override > env > file > default
+	if v, ok := c.overrideConfig[lower]; ok {
+		c.combinedConfig[lower] = v
+	} else if v, ok := c.envConfig[lower]; ok {
+		c.combinedConfig[lower] = ConfigMap{Key: key, Value: v.Value}
+	} else if v, ok := c.fileConfig[lower]; ok {
+		c.combinedConfig[lower] = v
 	} else {
-		c.combinedConfig[lower] = c.mapConfig[lower]
+		c.combinedConfig[lower] = ConfigMap{Key: key, Value: value}
 	}
 }