goext/reflectext/casting.go

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package reflectext
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import (
"reflect"
)
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var reflectBasicTypes = map[reflect.Kind]reflect.Type{
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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
}
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func TryCastType(v any, dest reflect.Type) (any, bool) {
underlying := Underlying(reflect.TypeOf(v))
if underlying != Underlying(dest) {
return nil, false
}
r1 := reflect.ValueOf(v)
if !r1.CanConvert(underlying) {
return nil, false
}
r2 := r1.Convert(underlying)
if !r2.CanConvert(dest) {
return nil, false
}
r4 := r2.Convert(dest)
return r4.Interface(), true
}