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 7 package slog
8 9 import (
10 "reflect"
11 "unsafe"
12 )
13 14 type (
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.
20 func StringValue(value string) Value {
21 hdr := (*reflect.StringHeader)(unsafe.Pointer(&value))
22 return Value{num: uint64(hdr.Len), any: stringptr(hdr.Data)}
23 }
24 25 func (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.
36 func (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.
50 func GroupValue(as ...Attr) Value {
51 hdr := (*reflect.SliceHeader)(unsafe.Pointer(&as))
52 return Value{num: uint64(hdr.Len), any: groupptr(hdr.Data)}
53 }
54