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// errchk $G -e $D/$F.go

// 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.

package main

func use(bool) {}

type T1 *int
type T2 *int

type T3 struct{ z []int }

var t3 T3

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)

        // Comparison of structs should have a good message
        use(t3 == t3) // ERROR "struct|expected"

        // 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"
        use(f == f) // ERROR "func can only be compared to nil"
        use(m == m) // ERROR "map can only be compared to nil"

        // 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"
}