v0.0.117

langext/reflection.go

@@ -0,0 +1,111 @@
+package langext
+
+import (
+	"reflect"
+)
+
+var reflectBasicTypes = []reflect.Type{
+	reflect.Bool:       reflect.TypeOf(false),
+	reflect.Int:        reflect.TypeOf(int(0)),
+	reflect.Int8:       reflect.TypeOf(int8(0)),
+	reflect.Int16:      reflect.TypeOf(int16(0)),
+	reflect.Int32:      reflect.TypeOf(int32(0)),
+	reflect.Int64:      reflect.TypeOf(int64(0)),
+	reflect.Uint:       reflect.TypeOf(uint(0)),
+	reflect.Uint8:      reflect.TypeOf(uint8(0)),
+	reflect.Uint16:     reflect.TypeOf(uint16(0)),
+	reflect.Uint32:     reflect.TypeOf(uint32(0)),
+	reflect.Uint64:     reflect.TypeOf(uint64(0)),
+	reflect.Uintptr:    reflect.TypeOf(uintptr(0)),
+	reflect.Float32:    reflect.TypeOf(float32(0)),
+	reflect.Float64:    reflect.TypeOf(float64(0)),
+	reflect.Complex64:  reflect.TypeOf(complex64(0)),
+	reflect.Complex128: reflect.TypeOf(complex128(0)),
+	reflect.String:     reflect.TypeOf(""),
+}
+
+// Underlying returns the underlying type of t (without type alias)
+//
+// https://github.com/golang/go/issues/39574#issuecomment-655664772
+func Underlying(t reflect.Type) (ret reflect.Type) {
+	if t.Name() == "" {
+		// t is an unnamed type. the underlying type is t itself
+		return t
+	}
+	kind := t.Kind()
+	if ret = reflectBasicTypes[kind]; ret != nil {
+		return ret
+	}
+	switch kind {
+	case reflect.Array:
+		ret = reflect.ArrayOf(t.Len(), t.Elem())
+	case reflect.Chan:
+		ret = reflect.ChanOf(t.ChanDir(), t.Elem())
+	case reflect.Map:
+		ret = reflect.MapOf(t.Key(), t.Elem())
+	case reflect.Func:
+		nIn := t.NumIn()
+		nOut := t.NumOut()
+		in := make([]reflect.Type, nIn)
+		out := make([]reflect.Type, nOut)
+		for i := 0; i < nIn; i++ {
+			in[i] = t.In(i)
+		}
+		for i := 0; i < nOut; i++ {
+			out[i] = t.Out(i)
+		}
+		ret = reflect.FuncOf(in, out, t.IsVariadic())
+	case reflect.Interface:
+		// not supported
+	case reflect.Ptr:
+		ret = reflect.PtrTo(t.Elem())
+	case reflect.Slice:
+		ret = reflect.SliceOf(t.Elem())
+	case reflect.Struct:
+		// only partially supported: embedded fields
+		// and unexported fields may cause panic in reflect.StructOf()
+		defer func() {
+			// if a panic happens, return t unmodified
+			if recover() != nil && ret == nil {
+				ret = t
+			}
+		}()
+		n := t.NumField()
+		fields := make([]reflect.StructField, n)
+		for i := 0; i < n; i++ {
+			fields[i] = t.Field(i)
+		}
+		ret = reflect.StructOf(fields)
+	}
+	return ret
+}
+
+// TryCast works similar to `v2, ok := v.(T)`
+// Except it works through type alias'
+func TryCast[T any](v any) (T, bool) {
+
+	underlying := Underlying(reflect.TypeOf(v))
+
+	def := *new(T)
+
+	if underlying != Underlying(reflect.TypeOf(def)) {
+		return def, false
+	}
+
+	r1 := reflect.ValueOf(v)
+
+	if !r1.CanConvert(underlying) {
+		return def, false
+	}
+
+	r2 := r1.Convert(underlying)
+
+	r3 := r2.Interface()
+
+	r4, ok := r3.(T)
+	if !ok {
+		return def, false
+	}
+
+	return r4, true
+}