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
