Compiling error when using struct literal in for loop

[Sheng Yu]

Hi,

I experienced a weird compiling error in my go program. I have such code snippet to reproduce it:

https://play.golang.org/p/0VSh02ng7p

package main

import "fmt"

type T struct {

Field int

}

func (t T) Next() T {

return T{t.Field+1}

}

func main() {

/* Got error at next for statement:

prog.go:14: syntax error: unexpected { at end of statement

prog.go:17: syntax error: non-declaration statement outside function body

for t := T{1}; t.Field < 10; t = t.Next() {

fmt.Println(t)

} */

// This is fine

t2 := T{1}

for ; t2.Field < 10; t2 = t2.Next() {

fmt.Println(t2)

}

}

I can understand the compiler may consider the first '{' be the beginning of a block. Do we consider it a bug? If the behavior is intentional, can we output less confusing error message?

Thanks.

Sheng

[Ian Lance Taylor]

Search for "ambiguity" in https://golang.org/ref/spec#Composite_literals .

You need to write
for t := (T{1}); t.Field < 10; t = t.Next() {

Yes, a better error message would be nice if possible. It's not easy,
though, as the parse failure is pretty far from the code that needs to
change.

Ian

[Sheng Yu]

Thanks for the pointer. It's good to have it in the spec already. 

Sheng