foreach on delegates incorrectly rejected

[dlangBugzillaToGithub]

Eyal reported this on 2017-06-06T22:43:12Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=17473

CC List

• ag0aep6g
• Vladimir Panteleev (@CyberShadow)
• Stanislav Blinov

Description

Here is an incorrect rejection of a valid program:

struct S {
    int f(int delegate(char a) dlg) {
        char c = cast(char)50;
        return dlg(c);
    }
}

unittest {
    S s;
    pragma(msg, typeof(&s.f));  // int delegate(int delegate(char a) dlg)
    foreach(x; &s.f) {}

    int delegate(int delegate(char a) dlg) g = &s.f;
    pragma(msg, typeof(g));     // int delegate(int delegate(char a) dlg)
    foreach(x; g) {}            // FAILS
}

[dlangBugzillaToGithub]

dlang-bugzilla (@CyberShadow) commented on 2017-06-07T13:26:14Z

Your example works here. Could you specify the compiler version and compilation flags?

[dlangBugzillaToGithub]

eyal commented on 2017-06-07T13:40:36Z

(In reply to Vladimir Panteleev from comment #1)
> Your example works here. Could you specify the compiler version and
> compilation flags?

dmd --version
DMD64 D Compiler v2.074.0
Copyright (c) 1999-2017 by Digital Mars written by Walter Bright

dmd -unittest testdlg.d
int delegate(int delegate(char a) dlg)
int delegate(int delegate(char a) dlg)
testdlg.d(15): Error: delegate g (int delegate(char a) dlg) is not callable using argument types (int delegate(ref char __applyArg0) pure nothrow @nogc @safe)


Perhaps you didn't pass -unittest?

[dlangBugzillaToGithub]

dlang-bugzilla (@CyberShadow) commented on 2017-06-07T13:42:50Z

(In reply to Eyal from comment #2)
> Perhaps you didn't pass -unittest?

Yep, my bad

[dlangBugzillaToGithub]

dlang-bugzilla (@CyberShadow) commented on 2017-06-07T13:44:24Z

Adding `ref` to `char a` fixes compilation, but it's still weird that `ref`'s presence is inconsistently needed.

[dlangBugzillaToGithub]

eyal commented on 2017-06-07T22:04:35Z

(In reply to Vladimir Panteleev from comment #4)
> Adding `ref` to `char a` fixes compilation, but it's still weird that
> `ref`'s presence is inconsistently needed.

It also changes the meaning of the program in an undesired way.

[dlangBugzillaToGithub]

stanislav.blinov commented on 2021-12-08T19:15:52Z

This probably should be changed to accepts-invalid instead. Foreach is documented as taking delegates with a ref parameter:

https://dlang.org/spec/statement.html#foreach-statement

...therefore that the line `foreach(x; &s.f);` compiles should be an error, shouldn't it?