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Source file test/typeswitch3.go

Documentation: test

     1  // errorcheck
     2  
     3  // Copyright 2011 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 erroneous type switches are caught be the compiler.
     8  // Issue 2700, among other things.
     9  // Does not compile.
    10  
    11  package main
    12  
    13  import (
    14  	"io"
    15  )
    16  
    17  type I interface {
    18  	M()
    19  }
    20  
    21  func main() {
    22  	var x I
    23  	switch x.(type) {
    24  	case string: // ERROR "impossible"
    25  		println("FAIL")
    26  	}
    27  
    28  	// Issue 2700: if the case type is an interface, nothing is impossible
    29  
    30  	var r io.Reader
    31  
    32  	_, _ = r.(io.Writer)
    33  
    34  	switch r.(type) {
    35  	case io.Writer:
    36  	}
    37  
    38  	// Issue 2827.
    39  	switch _ := r.(type) { // ERROR "invalid variable name _|no new variables"
    40  	}
    41  }
    42  
    43  func noninterface() {
    44  	var i int
    45  	switch i.(type) { // ERROR "cannot type switch on non-interface value"
    46  	case string:
    47  	case int:
    48  	}
    49  
    50  	type S struct {
    51  		name string
    52  	}
    53  	var s S
    54  	switch s.(type) { // ERROR "cannot type switch on non-interface value"
    55  	}
    56  }
    57  

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