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123 lines
3.3 KiB
Go
123 lines
3.3 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package opt
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import (
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"fmt"
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"reflect"
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jsonv2 "github.com/go-json-experiment/json"
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"github.com/go-json-experiment/json/jsontext"
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)
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// Value is an optional value to be JSON-encoded.
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// With [encoding/json], a zero Value is marshaled as a JSON null.
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// With [github.com/go-json-experiment/json], a zero Value is omitted from the
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// JSON object if the Go struct field specified with omitzero.
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// The omitempty tag option should never be used with Value fields.
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type Value[T any] struct {
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value T
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set bool
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}
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// Equal reports whether the receiver and the other value are equal.
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// If the template type T in Value[T] implements an Equal method, it will be used
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// instead of the == operator for comparing values.
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type equatable[T any] interface {
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// Equal reports whether the receiver and the other values are equal.
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Equal(other T) bool
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}
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// ValueOf returns an optional Value containing the specified value.
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// It treats nil slices and maps as empty slices and maps.
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func ValueOf[T any](v T) Value[T] {
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return Value[T]{value: v, set: true}
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}
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// String implements [fmt.Stringer].
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func (o *Value[T]) String() string {
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if !o.set {
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return fmt.Sprintf("(empty[%T])", o.value)
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}
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return fmt.Sprint(o.value)
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}
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// Set assigns the specified value to the optional value o.
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func (o *Value[T]) Set(v T) {
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*o = ValueOf(v)
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}
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// Clear resets o to an empty state.
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func (o *Value[T]) Clear() {
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*o = Value[T]{}
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}
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// IsSet reports whether o has a value set.
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func (o *Value[T]) IsSet() bool {
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return o.set
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}
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// Get returns the value of o.
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// If a value hasn't been set, a zero value of T will be returned.
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func (o Value[T]) Get() T {
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return o.value
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}
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// Get returns the value and a flag indicating whether the value is set.
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func (o Value[T]) GetOk() (v T, ok bool) {
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return o.value, o.set
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}
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// Equal reports whether o is equal to v.
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// Two optional values are equal if both are empty,
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// or if both are set and the underlying values are equal.
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// If the template type T implements an Equal(T) bool method, it will be used
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// instead of the == operator for value comparison.
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// If T is not comparable, it returns false.
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func (o Value[T]) Equal(v Value[T]) bool {
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if o.set != v.set {
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return false
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}
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if !o.set {
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return true
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}
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ov := any(o.value)
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if eq, ok := ov.(equatable[T]); ok {
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return eq.Equal(v.value)
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}
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if reflect.TypeFor[T]().Comparable() {
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return ov == any(v.value)
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}
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return false
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}
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// MarshalJSONV2 implements [jsonv2.MarshalerV2].
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func (o Value[T]) MarshalJSONV2(enc *jsontext.Encoder, opts jsonv2.Options) error {
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if !o.set {
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return enc.WriteToken(jsontext.Null)
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}
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return jsonv2.MarshalEncode(enc, &o.value, opts)
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}
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// UnmarshalJSONV2 implements [jsonv2.UnmarshalerV2].
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func (o *Value[T]) UnmarshalJSONV2(dec *jsontext.Decoder, opts jsonv2.Options) error {
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if dec.PeekKind() == 'n' {
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*o = Value[T]{}
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_, err := dec.ReadToken() // read null
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return err
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}
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o.set = true
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return jsonv2.UnmarshalDecode(dec, &o.value, opts)
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}
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// MarshalJSON implements [json.Marshaler].
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func (o Value[T]) MarshalJSON() ([]byte, error) {
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return jsonv2.Marshal(o) // uses MarshalJSONV2
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}
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// UnmarshalJSON implements [json.Unmarshaler].
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func (o *Value[T]) UnmarshalJSON(b []byte) error {
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return jsonv2.Unmarshal(b, o) // uses UnmarshalJSONV2
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}
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