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23bd214aee
The new comparison rule was added to the spec by changeset: 5605:33abb649cb63 user: Robert Griesemer <gri@golang.org> date: Thu Jun 03 16:55:50 2010 -0700 files: doc/go_spec.html description: go spec: Base comparison compatibility on assignment compatibility. Specifically: - Simplified definition of comparison compatibility and folded into section on comparison operators since it's only used there. This is a small language change/cleanup. As a consequence: - An interface value may now be compared against a non-interface value. - Channels with opposite directions cannot be compared directly anymore (per discussion with rsc). R=rsc, r, iant, ken2 CC=golang-dev https://golang.org/cl/1462041 but never implemented. Fixes #1070. R=ken2 CC=golang-dev https://golang.org/cl/2116047
130 lines
2.4 KiB
Go
130 lines
2.4 KiB
Go
// $G $D/$F.go && $L $F.$A && ./$A.out
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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 "unsafe"
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func use(bool) {}
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func stringptr(s string) uintptr { return *(*uintptr)(unsafe.Pointer(&s)) }
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func isfalse(b bool) {
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if b {
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// stack will explain where
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panic("wanted false, got true")
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}
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}
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func istrue(b bool) {
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if !b {
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// stack will explain where
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panic("wanted true, got false")
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}
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}
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type T *int
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func main() {
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var a []int
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var b map[string]int
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var c string = "hello"
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var d string = "hel" // try to get different pointer
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d = d + "lo"
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if stringptr(c) == stringptr(d) {
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panic("compiler too smart -- got same string")
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}
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var e = make(chan int)
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var ia interface{} = a
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var ib interface{} = b
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var ic interface{} = c
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var id interface{} = d
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var ie interface{} = e
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// these comparisons are okay because
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// string compare is okay and the others
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// are comparisons where the types differ.
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isfalse(ia == ib)
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isfalse(ia == ic)
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isfalse(ia == id)
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isfalse(ib == ic)
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isfalse(ib == id)
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istrue(ic == id)
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istrue(ie == ie)
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// these are okay because one side of the
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// comparison need only be assignable to the other.
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isfalse(a == ib)
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isfalse(a == ic)
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isfalse(a == id)
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isfalse(b == ic)
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isfalse(b == id)
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istrue(c == id)
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istrue(e == ie)
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isfalse(ia == b)
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isfalse(ia == c)
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isfalse(ia == d)
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isfalse(ib == c)
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isfalse(ib == d)
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istrue(ic == d)
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istrue(ie == e)
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// 6g used to let this go through as true.
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var g uint64 = 123
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var h int64 = 123
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var ig interface{} = g
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var ih interface{} = h
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isfalse(ig == ih)
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// map of interface should use == on interface values,
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// not memory.
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// TODO: should m[c], m[d] be valid here?
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var m = make(map[interface{}]int)
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m[ic] = 1
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m[id] = 2
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if m[ic] != 2 {
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println("m[ic] = ", m[ic])
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panic("bad m[ic]")
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}
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// non-interface comparisons
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{
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c := make(chan int)
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c1 := (<-chan int)(c)
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c2 := (chan<- int)(c)
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istrue(c == c1)
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istrue(c == c2)
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istrue(c1 == c)
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istrue(c2 == c)
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d := make(chan int)
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isfalse(c == d)
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isfalse(d == c)
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isfalse(d == c1)
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isfalse(d == c2)
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isfalse(c1 == d)
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isfalse(c2 == d)
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}
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// named types vs not
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{
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var x = new(int)
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var y T
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var z T = x
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isfalse(x == y)
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istrue(x == z)
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isfalse(y == z)
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isfalse(y == x)
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istrue(z == x)
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isfalse(z == y)
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}
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}
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