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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"
+}