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cmd/compile: fix OTYPESW Op comment

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OTYPESW Op comment says

  // List = Left.(type)

this seems to be wrong. Adding

  fmt.Printf("n: %v\n", cond)
  fmt.Printf("  n.List: %v\n", cond.List)
  fmt.Printf("  n.Left: %v\n", cond.Left)
  fmt.Printf("  n.Right: %v\n", cond.Right)

to (s *typeSwitch) walk(sw *Node), and compiling the following code
snippet

  var y interface{}
  switch x := y.(type) {
  default:
    println(x)
  }

prints

  n: <node TYPESW>
    n.List:
    n.Left: x
    n.Right: y

The correct OTYPESW Node field positions are

  // Left = Right.(type)

This is confirmed by the fact that, further in the code,
typeSwitch.walk() checks that Right (and not Left) is of type
interface:

  cond.Right = walkexpr(cond.Right, &sw.Ninit)
  if !cond.Right.Type.IsInterface() {
    yyerror("type switch must be on an interface")
    return
  }

This patch fixes the OTYPESW comment.

Change-Id: Ief1e409cfabb7640d7f7b0d4faabbcffaf605450
Reviewed-on: https://go-review.googlesource.com/69112
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Alberto Donizetti 2017-10-08 14:12:40 +02:00
parent 0c53b4ec4f
commit 07f7db3ea9
1 changed files with 1 additions and 1 deletions
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2
src/cmd/compile/internal/gc/syntax.go
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@ -571,7 +571,7 @@ const (
ORETURN // return List
OSELECT // select { List } (List is list of OXCASE or OCASE)
OSWITCH // switch Ninit; Left { List } (List is a list of OXCASE or OCASE)
OTYPESW // List = Left.(type) (appears as .Left of OSWITCH)
OTYPESW // Left = Right.(type) (appears as .Left of OSWITCH)
// types
OTCHAN // chan int