About bytes.NewBufferString(contents)

[TimLiuDream]

What version of Go are you using (go version)?

$ go version:1.10.3

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
set GOARCH=amd64

set GOBIN=

set GOCACHE=C:\Users\TimLiu\AppData\Local\go-build

set GOEXE=.exe

set GOHOSTARCH=amd64

set GOHOSTOS=windows

set GOOS=windows

set GOPATH=C:\Users\TimLiu\go

set GORACE=

set GOROOT=C:\Go

set GOTMPDIR=

set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64

set GCCGO=gccgo

set CC=gcc

set CXX=g++

set CGO_ENABLED=1

set CGO_CFLAGS=-g -O2

set CGO_CPPFLAGS=

set CGO_CXXFLAGS=-g -O2

set CGO_FFLAGS=-g -O2

set CGO_LDFLAGS=-g -O2

set PKG_CONFIG=pkg-config

set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\TimLiu\AppData\Local\Temp\go-build776041726=/tmp/go-build -gno-record-gcc-switches

What did you do?

var contents string
buffer1 := bytes.NewBufferString(contents)
fmt.Printf("The length of new buffer with contents %q: %d\n", contents, buffer1.Len())
fmt.Printf("The capacity of new buffer with contents %q: %d\n", contents, buffer1.Cap())
fmt.Println()

the result:

The length of new buffer with contents "": 0
The capacity of new buffer with contents "": 32

when i start write string:

	var contents string
	buffer1 := bytes.NewBufferString(contents)
	fmt.Printf("The length of new buffer with contents %q: %d\n", contents, buffer1.Len())
	fmt.Printf("The capacity of new buffer with contents %q: %d\n", contents, buffer1.Cap())
	fmt.Println()

	contents = "123456"
	fmt.Printf("Write contents %q ...\n", contents)
	buffer1.WriteString(contents)
	fmt.Printf("The length of buffer: %d\n", buffer1.Len())
	fmt.Printf("The capacity of buffer: %d\n", buffer1.Cap())
	fmt.Println()

the result is ：

The length of new buffer with contents "": 0
The capacity of new buffer with contents "": 0

Write contents "123456" ...
The length of buffer: 6
The capacity of buffer: 6

why the initial capacity is Different？

What did you expect to see?

i think the initial capacity is always zero

What did you see instead?

[ianlancetaylor]

See #24163. We don't make any promises about the capacity of a slice created from a string. Why should we?