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https://github.com/golang/go
synced 2024-09-25 07:30:13 -06:00
d03611f628
An experiment: allow structs to be copied even if they contain unexported fields. This gives packages the ability to return opaque values in their APIs, like reflect does for reflect.Value but without the kludgy hacks reflect resorts to. In general, we trust programmers not to do silly things like *x = *y on a package's struct pointers, just as we trust programmers not to do unicode.Letter = unicode.Digit, but packages that want a harder guarantee can introduce an extra level of indirection, like in the changes to os.File in this CL or by using an interface type. All in one CL so that it can be rolled back more easily if we decide this is a bad idea. Originally discussed in March 2011. https://groups.google.com/group/golang-dev/t/3f5d30938c7c45ef R=golang-dev, adg, dvyukov, r, bradfitz, jan.mercl, gri CC=golang-dev https://golang.org/cl/5372095
54 lines
731 B
Go
54 lines
731 B
Go
// errchk $G -e $D/$F.go
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import "sync"
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type T struct {
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int
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sync.Mutex
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}
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func main() {
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{
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var x, y sync.Mutex
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x = y // ok
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_ = x
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}
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{
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var x, y T
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x = y // ok
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_ = x
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}
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{
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var x, y [2]sync.Mutex
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x = y // ok
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_ = x
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}
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{
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var x, y [2]T
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x = y // ok
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_ = x
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}
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{
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x := sync.Mutex{0, 0} // ERROR "assignment.*Mutex"
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_ = x
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}
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{
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x := sync.Mutex{key: 0} // ERROR "(unknown|assignment).*Mutex"
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_ = x
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}
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{
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x := &sync.Mutex{} // ok
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var y sync.Mutex // ok
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y = *x // ok
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*x = y // ok
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_ = x
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_ = y
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}
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}
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