cty: add cty.GoIter for Go 1.23+

cty/element_iterator.go

@@ -6,16 +6,34 @@ import (
 	"github.com/zclconf/go-cty/cty/set"
 )
 
+// GoIter returns a [iter.Seq2[cty.Value, cty.Value]] iterator that iterates over
+// the elements of a collection-typed value, yielding each element's key and
+// value in turn.
+// From Go 1.23, this can be used as follows:
+//
+//	for key, val := range cty.GoIter(val) {
+//		// ...
+//	}
+func GoIter(val Value) func(yield func(Value, Value) bool) {
+	return func(yield func(Value, Value) bool) {
+		for it := val.ElementIterator(); it.Next(); {
+			if !yield(it.Element()) {
+				return
+			}
+		}
+	}
+}
+
 // ElementIterator is the interface type returned by Value.ElementIterator to
 // allow the caller to iterate over elements of a collection-typed value.
 //
 // Its usage pattern is as follows:
 //
-//     it := val.ElementIterator()
-//     for it.Next() {
-//         key, val := it.Element()
-//         // ...
-//     }
+//	it := val.ElementIterator()
+//	for it.Next() {
+//		key, val := it.Element()
+//		// ...
+//	}
 type ElementIterator interface {
 	Next() bool
 	Element() (key Value, value Value)

cty/element_iterator_test.go

@@ -0,0 +1,29 @@
+//go:build go1.23
+
+package cty_test
+
+import (
+	"fmt"
+
+	"github.com/zclconf/go-cty/cty"
+)
+
+func ExampleGoIter() {
+	// Test that iterating over a list works
+	listVal := cty.ListVal([]cty.Value{cty.NumberIntVal(1), cty.NumberIntVal(2)})
+	for key, val := range cty.GoIter(listVal) {
+		fmt.Println(key.GoString(), val.GoString())
+	}
+	keyVal := cty.MapVal(map[string]cty.Value{
+		"a": cty.NumberIntVal(1),
+		"b": cty.NumberIntVal(2),
+	})
+	for key, val := range cty.GoIter(keyVal) {
+		fmt.Println(key.GoString(), val.GoString())
+	}
+	// Output:
+	// cty.NumberIntVal(0) cty.NumberIntVal(1)
+	// cty.NumberIntVal(1) cty.NumberIntVal(2)
+	// cty.StringVal("a") cty.NumberIntVal(1)
+	// cty.StringVal("b") cty.NumberIntVal(2)
+}