/usr/share/go-1.10/src/strings/builder.go is in golang-1.10-src 1.10.1-1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 | // Copyright 2017 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.
package strings
import (
"unicode/utf8"
"unsafe"
)
// A Builder is used to efficiently build a string using Write methods.
// It minimizes memory copying. The zero value is ready to use.
// Do not copy a non-zero Builder.
type Builder struct {
addr *Builder // of receiver, to detect copies by value
buf []byte
}
// noescape hides a pointer from escape analysis. noescape is
// the identity function but escape analysis doesn't think the
// output depends on the input. noescape is inlined and currently
// compiles down to zero instructions.
// USE CAREFULLY!
// This was copied from the runtime; see issues 23382 and 7921.
//go:nosplit
func noescape(p unsafe.Pointer) unsafe.Pointer {
x := uintptr(p)
return unsafe.Pointer(x ^ 0)
}
func (b *Builder) copyCheck() {
if b.addr == nil {
// This hack works around a failing of Go's escape analysis
// that was causing b to escape and be heap allocated.
// See issue 23382.
// TODO: once issue 7921 is fixed, this should be reverted to
// just "b.addr = b".
b.addr = (*Builder)(noescape(unsafe.Pointer(b)))
} else if b.addr != b {
panic("strings: illegal use of non-zero Builder copied by value")
}
}
// String returns the accumulated string.
func (b *Builder) String() string {
return *(*string)(unsafe.Pointer(&b.buf))
}
// Len returns the number of accumulated bytes; b.Len() == len(b.String()).
func (b *Builder) Len() int { return len(b.buf) }
// Reset resets the Builder to be empty.
func (b *Builder) Reset() {
b.addr = nil
b.buf = nil
}
// grow copies the buffer to a new, larger buffer so that there are at least n
// bytes of capacity beyond len(b.buf).
func (b *Builder) grow(n int) {
buf := make([]byte, len(b.buf), 2*cap(b.buf)+n)
copy(buf, b.buf)
b.buf = buf
}
// Grow grows b's capacity, if necessary, to guarantee space for
// another n bytes. After Grow(n), at least n bytes can be written to b
// without another allocation. If n is negative, Grow panics.
func (b *Builder) Grow(n int) {
b.copyCheck()
if n < 0 {
panic("strings.Builder.Grow: negative count")
}
if cap(b.buf)-len(b.buf) < n {
b.grow(n)
}
}
// Write appends the contents of p to b's buffer.
// Write always returns len(p), nil.
func (b *Builder) Write(p []byte) (int, error) {
b.copyCheck()
b.buf = append(b.buf, p...)
return len(p), nil
}
// WriteByte appends the byte c to b's buffer.
// The returned error is always nil.
func (b *Builder) WriteByte(c byte) error {
b.copyCheck()
b.buf = append(b.buf, c)
return nil
}
// WriteRune appends the UTF-8 encoding of Unicode code point r to b's buffer.
// It returns the length of r and a nil error.
func (b *Builder) WriteRune(r rune) (int, error) {
b.copyCheck()
if r < utf8.RuneSelf {
b.buf = append(b.buf, byte(r))
return 1, nil
}
l := len(b.buf)
if cap(b.buf)-l < utf8.UTFMax {
b.grow(utf8.UTFMax)
}
n := utf8.EncodeRune(b.buf[l:l+utf8.UTFMax], r)
b.buf = b.buf[:l+n]
return n, nil
}
// WriteString appends the contents of s to b's buffer.
// It returns the length of s and a nil error.
func (b *Builder) WriteString(s string) (int, error) {
b.copyCheck()
b.buf = append(b.buf, s...)
return len(s), nil
}
|