Type system hole: escaping inout delegates

[dlangBugzillaToGithub]

timon.gehr reported this on 2017-08-11T15:36:42Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=17743

CC List

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

Description

DMD v.2075.0:

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

inout(int)* delegate(inout(int)*) dg;
inout(int)* prepare(inout(int)* x){
    dg = y=>x;
    return x;
}
void main(){
    prepare(&b);
    int* y=dg(&a);
    assert(&b is y); // passes. ouch.
    *y=3;
    assert(b is *&b); // fails!
}

[dlangBugzillaToGithub]

schveiguy (@schveiguy) commented on 2017-08-14T13:32:14Z

This is why inout data is not allowed to be stored as a global (which essentially you have done). Basically, inout data should not be allowed to escape the function except via the parameters or return, where it is properly handled.

[dlangBugzillaToGithub]

dfj1esp02 commented on 2021-12-13T13:36:57Z

As I understand, it's due to decision that nested functions use inout qialifier of the outer function. Then an easy way to fix this is to disallow conversion of such nested function to inout-typed delegate.