72 lines
1.9 KiB
Go
72 lines
1.9 KiB
Go
// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package mak helps make maps. It contains generic helpers to make/assign
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// things, notably to maps, but also slices.
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package mak
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import (
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"fmt"
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"reflect"
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)
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// Set populates an entry in a map, making the map if necessary.
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//
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// That is, it assigns (*m)[k] = v, making *m if it was nil.
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func Set[K comparable, V any, T ~map[K]V](m *T, k K, v V) {
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if *m == nil {
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*m = make(map[K]V)
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}
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(*m)[k] = v
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}
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// NonNil takes a pointer to a Go data structure
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// (currently only a slice or a map) and makes sure it's non-nil for
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// JSON serialization. (In particular, JavaScript clients usually want
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// the field to be defined after they decode the JSON.)
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//
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// Deprecated: use NonNilSliceForJSON or NonNilMapForJSON instead.
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func NonNil(ptr interface{}) {
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if ptr == nil {
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panic("nil interface")
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}
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rv := reflect.ValueOf(ptr)
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if rv.Kind() != reflect.Ptr {
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panic(fmt.Sprintf("kind %v, not Ptr", rv.Kind()))
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}
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if rv.Pointer() == 0 {
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panic("nil pointer")
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}
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rv = rv.Elem()
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if rv.Pointer() != 0 {
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return
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}
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switch rv.Type().Kind() {
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case reflect.Slice:
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rv.Set(reflect.MakeSlice(rv.Type(), 0, 0))
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case reflect.Map:
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rv.Set(reflect.MakeMap(rv.Type()))
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}
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}
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// NonNilSliceForJSON makes sure that *slicePtr is non-nil so it will
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// won't be omitted from JSON serialization and possibly confuse JavaScript
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// clients expecting it to be present.
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func NonNilSliceForJSON[T any, S ~[]T](slicePtr *S) {
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if *slicePtr != nil {
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return
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}
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*slicePtr = make([]T, 0)
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}
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// NonNilMapForJSON makes sure that *slicePtr is non-nil so it will
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// won't be omitted from JSON serialization and possibly confuse JavaScript
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// clients expecting it to be present.
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func NonNilMapForJSON[K comparable, V any, M ~map[K]V](mapPtr *M) {
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if *mapPtr != nil {
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return
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}
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*mapPtr = make(M)
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}
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