On Sat, Aug 26, 2023 at 2:11 PM Mike Schinkel <m...@newclarity.net> wrote:
>
> Question about disallowing `goto <label>` jumping over a variable declaration?
>
>
> And please, before bikeshedding opinions about the use of `goto` pro or con —
> note that the Go standard library uses `goto` in some places — this question
> is purely for me to gain better understanding the choices made with the Go
> compiler.
>
>
> Question. Was it:
>
>
> 1. Somehow logically required by the compiler, and if so can you elaborate
> why?
>
> 2. A design decision made, and if so what what the rationale for the design
> decision?
>
> 3. A limitation place on GoLang for some other reason, and if so, what and
> why?
>
>
> I have prepared an example showing use of `goto` that compiles and one that
> does not at this playground URL:
>
>
> https://goplay.tools/snippet/tSAbWhmiCZK
>
>
> Hoping to hear from someone who actually knows why the decision was made as
> opposed to someone who might just be guessing at the reason.
Consider a function like
func F() {
goto lab
x := 1
lab:
fmt.Println(x)
}
This function is forbidden today. If it were permitted, what should it print?
If the answer to that question seems obvious, what about a case like
func F() {
goto lab
x := func() int {
fmt.Println("setting x")
return 1
}()
lab:
fmt.Println(x)
}
Should that print "setting x"?
Rather than attempt to answer these kinds of questions, Go simply
forbids cases like this.
Note that Go is not the only language with this restriction. This
similar C++ function is invalid, because the goto crosses the
initialization of the variable.
int f() {
goto lab;
int x = 1;
lab:
std::cout << x;
return 0;
}
If you are interested in this topic you may be interested in
https://go.dev/issue/27165 and https://go.dev/issue/26058.
Ian
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