alias this produces an infinite range when used with ranges

[dlangBugzillaToGithub]

Andrej Mitrovic (@AndrejMitrovic) reported this on 2019-10-02T02:07:19Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=20258

CC List

• berni44 (@WalterBright)

Description

-----
import std.stdio;

struct Set
{
    int[int] set;
    auto walk () { return this.set.byKey(); }
    alias walk this;
}

void main()
{
    Set set;
    set.set[1] = 10;
    writefln("Set contents: %s", set.set.byKey());  // ok
    writefln("Set contents: %s", set);  // prints "1" infinitely
}
-----

Tested with v2.086.1 and v2.088.0

[dlangBugzillaToGithub]

bugzilla (@WalterBright) commented on 2019-12-03T10:09:45Z

I think, the bug is to be found in dmd and byKey is innocent. If not, the correct component is not phobos but druntime, because byKey is located there.

[dlangBugzillaToGithub]

andrej.mitrovich (@AndrejMitrovic) commented on 2022-07-07T13:25:29Z

Simpler example:

-----
import std.stdio;
import std.range;

struct Set
{
    auto walk () { return [].only; }
    alias walk this;
}

void main()
{
    Set set;
    writeln(set);
}
-----

It has to do with ranges, not specifically hashmaps as previously thought.

I think somewhere in the formatter it's probably trying to invoke walk() multiple times, implicitly through that 'alias this'.