Type system hole: returning inout delegates

[dlangBugzillaToGithub]

timon.gehr reported this on 2017-08-11T15:41:13Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=17744

CC List

• Walter Bright (@WalterBright)
• Steven Schveighoffer (@schveiguy)

Description

DMD v2.075.0:

@safe:
int a;
immutable(int) b=2;

inout(int)* delegate(inout(int)*)@safe delegate()@safe foo(inout(int)* y){
    inout(int)* bar(inout(int)* p){
        return y;
    }
    return ()=>&bar;
}
void main(){
    int* y=foo(&b)()(&a);
    *y=3;
    assert(&b is y); // passes. ouch.
    assert(b is *&b); // fails!
}

If &bar is returned directly instead of ()=>&bar, DMD applies a strange work-around (it replaces `inout` in the returned delegate by `const`).