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// errorcheck
// Copyright 2010 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.
// Verify that incorrect comparisons are detected.
// Does not compile.
package main
func use(bool) {}
type T1 *int
type T2 *int
type T3 struct{ z []int }
var t3 T3
type T4 struct {
_ []int
a float64
}
var t4 T4
func main() {
// Arguments to comparison must be
// assignable one to the other (or vice versa)
// so chan int can be compared against
// directional channels but channel of different
// direction cannot be compared against each other.
var c1 chan<- int
var c2 <-chan int
var c3 chan int
use(c1 == c2) // ERROR "invalid operation|incompatible"
use(c2 == c1) // ERROR "invalid operation|incompatible"
use(c1 == c3)
use(c2 == c2)
use(c3 == c1)
use(c3 == c2)
// Same applies to named types.
var p1 T1
var p2 T2
var p3 *int
use(p1 == p2) // ERROR "invalid operation|incompatible"
use(p2 == p1) // ERROR "invalid operation|incompatible"
use(p1 == p3)
use(p2 == p2)
use(p3 == p1)
use(p3 == p2)
// Arrays are comparable if and only if their element type is comparable.
var a1 [1]int
var a2 [1]func()
var a3 [0]func()
use(a1 == a1)
use(a2 == a2) // ERROR "invalid operation|invalid comparison"
use(a3 == a3) // ERROR "invalid operation|invalid comparison"
// Comparison of structs should have a good message
use(t3 == t3) // ERROR "struct|expected|cannot compare"
use(t4 == t4) // ERROR "cannot be compared|non-comparable|cannot compare"
// Slices, functions, and maps too.
var x []int
var f func()
var m map[int]int
use(x == x) // ERROR "slice can only be compared to nil|cannot compare"
use(f == f) // ERROR "func can only be compared to nil|cannot compare"
use(m == m) // ERROR "map can only be compared to nil|cannot compare"
// Comparison with interface that cannot return true
// (would panic).
var i interface{}
use(i == x) // ERROR "invalid operation"
use(x == i) // ERROR "invalid operation"
use(i == f) // ERROR "invalid operation"
use(f == i) // ERROR "invalid operation"
use(i == m) // ERROR "invalid operation"
use(m == i) // ERROR "invalid operation"
}