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      1 // errorcheck
      2 
      3 // Copyright 2010 The Go Authors. All rights reserved.
      4 // Use of this source code is governed by a BSD-style
      5 // license that can be found in the LICENSE file.
      6 
      7 // Verify that incorrect comparisons are detected.
      8 // Does not compile.
      9 
     10 package main
     11 
     12 func use(bool) {}
     13 
     14 type T1 *int
     15 type T2 *int
     16 
     17 type T3 struct{ z []int }
     18 
     19 var t3 T3
     20 
     21 type T4 struct {
     22 	_ []int
     23 	a float64
     24 }
     25 
     26 var t4 T4
     27 
     28 func main() {
     29 	// Arguments to comparison must be
     30 	// assignable one to the other (or vice versa)
     31 	// so chan int can be compared against
     32 	// directional channels but channel of different
     33 	// direction cannot be compared against each other.
     34 	var c1 chan<- int
     35 	var c2 <-chan int
     36 	var c3 chan int
     37 
     38 	use(c1 == c2) // ERROR "invalid operation|incompatible"
     39 	use(c2 == c1) // ERROR "invalid operation|incompatible"
     40 	use(c1 == c3)
     41 	use(c2 == c2)
     42 	use(c3 == c1)
     43 	use(c3 == c2)
     44 
     45 	// Same applies to named types.
     46 	var p1 T1
     47 	var p2 T2
     48 	var p3 *int
     49 
     50 	use(p1 == p2) // ERROR "invalid operation|incompatible"
     51 	use(p2 == p1) // ERROR "invalid operation|incompatible"
     52 	use(p1 == p3)
     53 	use(p2 == p2)
     54 	use(p3 == p1)
     55 	use(p3 == p2)
     56 
     57 	// Arrays are comparable if and only if their element type is comparable.
     58 	var a1 [1]int
     59 	var a2 [1]func()
     60 	var a3 [0]func()
     61 	use(a1 == a1)
     62 	use(a2 == a2) // ERROR "invalid operation|invalid comparison"
     63 	use(a3 == a3) // ERROR "invalid operation|invalid comparison"
     64 
     65 	// Comparison of structs should have a good message
     66 	use(t3 == t3) // ERROR "struct|expected"
     67 	use(t4 == t4) // ERROR "cannot be compared|non-comparable"
     68 
     69 	// Slices, functions, and maps too.
     70 	var x []int
     71 	var f func()
     72 	var m map[int]int
     73 	use(x == x) // ERROR "slice can only be compared to nil"
     74 	use(f == f) // ERROR "func can only be compared to nil"
     75 	use(m == m) // ERROR "map can only be compared to nil"
     76 
     77 	// Comparison with interface that cannot return true
     78 	// (would panic).
     79 	var i interface{}
     80 	use(i == x) // ERROR "invalid operation"
     81 	use(x == i) // ERROR "invalid operation"
     82 	use(i == f) // ERROR "invalid operation"
     83 	use(f == i) // ERROR "invalid operation"
     84 	use(i == m) // ERROR "invalid operation"
     85 	use(m == i) // ERROR "invalid operation"
     86 }
     87