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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build go1.19 && !go1.20
package slog
import (
"reflect"
"unsafe"
)
type (
stringptr unsafe.Pointer // used in Value.any when the Value is a string
groupptr unsafe.Pointer // used in Value.any when the Value is a []Attr
)
// StringValue returns a new Value for a string.
func StringValue(value string) Value {
hdr := (*reflect.StringHeader)(unsafe.Pointer(&value))
return Value{num: uint64(hdr.Len), any: stringptr(hdr.Data)}
}
func (v Value) str() string {
var s string
hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))
hdr.Data = uintptr(v.any.(stringptr))
hdr.Len = int(v.num)
return s
}
// String returns Value's value as a string, formatted like fmt.Sprint. Unlike
// the methods Int64, Float64, and so on, which panic if v is of the
// wrong kind, String never panics.
func (v Value) String() string {
if sp, ok := v.any.(stringptr); ok {
// Inlining this code makes a huge difference.
var s string
hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))
hdr.Data = uintptr(sp)
hdr.Len = int(v.num)
return s
}
return string(v.append(nil))
}
// GroupValue returns a new Value for a list of Attrs.
// The caller must not subsequently mutate the argument slice.
func GroupValue(as ...Attr) Value {
hdr := (*reflect.SliceHeader)(unsafe.Pointer(&as))
return Value{num: uint64(hdr.Len), any: groupptr(hdr.Data)}
}
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