Multiple return values of function can't be correctly handled by fmt.Println #662
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The spec is not very precise about what should happen when you pass a function
returning two results as the actual parameter for a ...T formal parameter. We should
be clarifying this.
Superficially, this looks like a compiler bug. The following modification of your
program seems to hang:
package main
import (
"fmt"
)
// Foo and Bar are never actually called
// If they were commented out, the wrong behavior will disappear
func foo(string) ([]byte, bool) { return nil, false }
func bar() { fmt.Println(foo("test")) }
func sample_data() ([]byte, bool) { return []byte{1, 2, 3}, false }
func println(args ... interface{}) {
println("len = ", len(args))
}
func main() {
// This is correct of course
//fmt.Println([]byte{1, 2, 3}, false)
println([]byte{1, 2, 3}, false)
// If we reference the return value at first, it works fine
r, e := sample_data()
//fmt.Println(r, e)
println(r, e)
//fmt.Println(sample_data()) // <-- strange result happens
println(sample_data()) // <-- strange result happens
}
Owner changed to r...@golang.org. |
The modified version I should have used is this one:
package main
import (
"fmt"
)
// Foo and Bar are never actually called
// If they were commented out, the wrong behavior will disappear
func foo(string) ([]byte, bool) { return nil, false }
func bar() { fmt.Println(foo("test")) }
func sample_data() ([]byte, bool) { return []byte{1, 2, 3}, false }
func f(args ... interface{}) {
println("len = ", len(args))
}
func main() {
// This is correct of course
//fmt.Println([]byte{1, 2, 3}, false)
f([]byte{1, 2, 3}, false)
// If we reference the return value at first, it works fine
r, e := sample_data()
//fmt.Println(r, e)
f(r, e)
//fmt.Println(sample_data()) // <-- strange result happens
f(sample_data()) // <-- strange result happens
}
which doesn't hang. It appears that the previous version was calling the built-in
println instead of the user-defined one (which would be another compiler bug).
|
|
This issue was closed by revision 253fd30. Status changed to Fixed. |
This issue was closed.
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by hou.danwu:
What steps will reproduce the problem? --------------- Compile and run the attached program What is the expected output? What do you see instead? --------------- Expected: [1 2 3] false [1 2 3] false [1 2 3] false Got: [1 2 3] false [1 2 3] false {[] true} What is your $GOOS? $GOARCH? -------------- $GOOS=linux $GOARCH=386 Which revision are you using? (hg identify) -------------- changeset: 5040:bd4b0edb8c55 tag: tip Please provide any additional information below.Attachments:
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