reflect: add Cap and Len support for map and chan

Author: cornelk

src/reflect/value.go

@@ -304,29 +304,48 @@ func (v Value) Slice(i, j int) Value {
 	panic("unimplemented: (reflect.Value).Slice()")
 }
 
+//go:linkname maplen runtime.hashmapLenUnsafePointer
+func maplen(p unsafe.Pointer) int
+
+//go:linkname chanlen runtime.chanLenUnsafePointer
+func chanlen(p unsafe.Pointer) int
+
 // Len returns the length of this value for slices, strings, arrays, channels,
-// and maps. For oter types, it panics.
+// and maps. For other types, it panics.
 func (v Value) Len() int {
 	t := v.Type()
 	switch t.Kind() {
+	case Array:
+		return v.Type().Len()
+	case Chan:
+		return chanlen(v.value)
+	case Map:
+		return maplen(v.value)
 	case Slice:
 		return int((*SliceHeader)(v.value).Len)
 	case String:
 		return int((*StringHeader)(v.value).Len)
-	case Array:
-		return v.Type().Len()
-	default: // Chan, Map
-		panic("unimplemented: (reflect.Value).Len()")
+	default:
+		panic(&ValueError{"Len"})
 	}
 }
 
+//go:linkname chancap runtime.chanCapUnsafePointer
+func chancap(p unsafe.Pointer) int
+
+// Cap returns the capacity of this value for arrays, channels and slices.
+// For other types, it panics.
 func (v Value) Cap() int {
 	t := v.Type()
 	switch t.Kind() {
+	case Array:
+		return v.Type().Len()
+	case Chan:
+		return chancap(v.value)
 	case Slice:
 		return int((*SliceHeader)(v.value).Cap)
-	default: // Array, Chan
-		panic("unimplemented: (reflect.Value).Cap()")
+	default:
+		panic(&ValueError{"Cap"})
 	}
 }
 

src/runtime/hashmap.go

@@ -1,7 +1,7 @@
 package runtime
 
 // This is a hashmap implementation for the map[T]T type.
-// It is very rougly based on the implementation of the Go hashmap:
+// It is very roughly based on the implementation of the Go hashmap:
 //
 //     https://golang.org/src/runtime/map.go
 
@@ -80,13 +80,20 @@ func hashmapMake(keySize, valueSize uint8, sizeHint uintptr) *hashmap {
 
 // Return the number of entries in this hashmap, called from the len builtin.
 // A nil hashmap is defined as having length 0.
+//go:inline
 func hashmapLen(m *hashmap) int {
 	if m == nil {
 		return 0
 	}
 	return int(m.count)
 }
 
+// wrapper for use in reflect
+func hashmapLenUnsafePointer(p unsafe.Pointer) int {
+	m := (*hashmap)(p)
+	return hashmapLen(m)
+}
+
 // Set a specified key to a given value. Grow the map if necessary.
 //go:nobounds
 func hashmapSet(m *hashmap, key unsafe.Pointer, value unsafe.Pointer, hash uint32, keyEqual func(x, y unsafe.Pointer, n uintptr) bool) {