Fixed updating array bug (Issue 3 in git)

Handle 'index out of range' errors more gracefully

README.md

@@ -3,6 +3,12 @@ yaml is a lightweight and flexible command-line YAML processor
 
 The aim of the project is to be the [jq](https://github.com/stedolan/jq) or sed of yaml files.
 
+## Install
+[Download latest binary](https://github.com/mikefarah/yaml/releases/latest) or alternatively:
+```
+go get github.com/mikefarah/yaml
+```
+
 ## Features
 - Written in portable go, so you can download a lovely dependency free binary
 - Deep read a yaml file with a given path
@@ -11,11 +17,6 @@ The aim of the project is to be the [jq](https://github.com/stedolan/jq) or sed
 - Convert from json to yaml
 - Convert from yaml to json
 
-[Download latest binary](https://github.com/mikefarah/yaml/releases/latest) or alternatively:
-```
-go get github.com/mikefarah/yaml
-```
-
 ## Read examples
 ```
 yaml r <yaml file> <path>

data_navigator.go

@@ -9,11 +9,25 @@ func write(context map[interface{}]interface{}, head string, tail []string, valu
 	if len(tail) == 0 {
 		context[head] = value
 	} else {
-		// e.g. if updating a.b.c, we need to get the 'b' map...
-		toUpdate := readMap(context, head, tail[0:len(tail)-1]).(map[interface{}]interface{})
-		//  and then set the 'c' key.
-		key := (tail[len(tail)-1])
-		toUpdate[key] = value
+		// e.g. if updating a.b.c, we need to get the 'b', this could be a map or an array
+		var parent = readMap(context, head, tail[0:len(tail)-1])
+		switch parent.(type) {
+		case map[interface{}]interface{}:
+			toUpdate := parent.(map[interface{}]interface{})
+			// b is a map, update the key 'c' to the supplied value
+			key := (tail[len(tail)-1])
+			toUpdate[key] = value
+		case []interface{}:
+			toUpdate := parent.([]interface{})
+			// b is an array, update it at index 'c' to the supplied value
+			rawIndex := (tail[len(tail)-1])
+			index, err := strconv.ParseInt(rawIndex, 10, 64)
+			if err != nil {
+				die("Error accessing array: %v", err)
+			}
+			toUpdate[index] = value
+		}
+
 	}
 }
 
@@ -58,7 +72,7 @@ func recurse(value interface{}, head string, tail []string) interface{} {
 }
 
 func readArray(array []interface{}, head int64, tail []string) interface{} {
-	if head > int64(len(array)) {
+	if head >= int64(len(array)) {
 		return nil
 	}
 

data_navigator_test.go

@@ -83,6 +83,17 @@ b:
 	assertResult(t, nil, readMap(data, "b", []string{"d", "3"}))
 }
 
+func TestReadMap_with_array_out_of_bounds_by_1(t *testing.T) {
+	var data = parseData(`
+---
+b:
+  d:
+    - 3
+    - 4
+`)
+	assertResult(t, nil, readMap(data, "b", []string{"d", "2"}))
+}
+
 func TestReadMap_with_array_splat(t *testing.T) {
 	var data = parseData(`
 e:
@@ -108,6 +119,18 @@ b:
 	assertResult(t, "4", b["c"].(string))
 }
 
+func TestWrite_array(t *testing.T) {
+	var data = parseData(`
+b:
+  - aa
+`)
+
+	write(data, "b", []string{"0"}, "bb")
+
+	b := data["b"].([]interface{})
+	assertResult(t, "bb", b[0].(string))
+}
+
 func TestWrite_with_no_tail(t *testing.T) {
 	var data = parseData(`
 b: