1// Copyright 2022 The Go Authors. All rights reserved.
 2// Use of this source code is governed by a BSD-style
 3// license that can be found in the LICENSE file.
 4
 5//go:build go1.19 && !go1.20
 6
 7package slog
 8
 9import (
10	"reflect"
11	"unsafe"
12)
13
14type (
15	stringptr unsafe.Pointer // used in Value.any when the Value is a string
16	groupptr  unsafe.Pointer // used in Value.any when the Value is a []Attr
17)
18
19// StringValue returns a new Value for a string.
20func StringValue(value string) Value {
21	hdr := (*reflect.StringHeader)(unsafe.Pointer(&value))
22	return Value{num: uint64(hdr.Len), any: stringptr(hdr.Data)}
23}
24
25func (v Value) str() string {
26	var s string
27	hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))
28	hdr.Data = uintptr(v.any.(stringptr))
29	hdr.Len = int(v.num)
30	return s
31}
32
33// String returns Value's value as a string, formatted like fmt.Sprint. Unlike
34// the methods Int64, Float64, and so on, which panic if v is of the
35// wrong kind, String never panics.
36func (v Value) String() string {
37	if sp, ok := v.any.(stringptr); ok {
38		// Inlining this code makes a huge difference.
39		var s string
40		hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))
41		hdr.Data = uintptr(sp)
42		hdr.Len = int(v.num)
43		return s
44	}
45	return string(v.append(nil))
46}
47
48// GroupValue returns a new Value for a list of Attrs.
49// The caller must not subsequently mutate the argument slice.
50func GroupValue(as ...Attr) Value {
51	hdr := (*reflect.SliceHeader)(unsafe.Pointer(&as))
52	return Value{num: uint64(hdr.Len), any: groupptr(hdr.Data)}
53}