foreach on matrix literal refuses immutable iteration

[dlangBugzillaToGithub]

bearophile_hugs reported this on 2013-08-24T08:55:18Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=10880

CC List

• Meta
• yebblies

Description

A matrix literal can be assigned to an immutable, but this isn't done in a foreach:


void main() {
    immutable m1 = [[1]]; // OK
    foreach (immutable v; [[1]]) {} // error
}


dmd 2.064alpha gives:

test.d(3): Error: cannot implicitly convert expression (__aggr4[__key5]) of type int[] to immutable(int[])

[dlangBugzillaToGithub]

yebblies commented on 2013-11-20T07:44:52Z

And nor should it.  As the error says, [[1]] has type int[][], and you can't implicitly convert int[] to immutable(int[]).

Asking for initializer-style type inference is an enhancement, and doesn't work particularly well with the way foreach expands to for.

Alternatives are to use const, or give the aggregate expression an explicit type.

[dlangBugzillaToGithub]

bearophile_hugs commented on 2013-11-20T08:07:34Z

(In reply to comment #1)

> Asking for initializer-style type inference is an enhancement,

OK.


> and doesn't work
> particularly well with the way foreach expands to for.

If you think this enhancement request is too much work to implement, or it causes other troubles, then close this ER down.

[dlangBugzillaToGithub]

monkeyworks12 commented on 2013-11-20T14:25:52Z

(In reply to comment #1)
> And nor should it.  As the error says, [[1]] has type int[][], and you can't
> implicitly convert int[] to immutable(int[]).
> 
> Asking for initializer-style type inference is an enhancement, and doesn't work
> particularly well with the way foreach expands to for.
> 
> Alternatives are to use const, or give the aggregate expression an explicit
> type.

In this case, isn't [[1]] a unique expression, so it can be implicitly cast to immutable? Also, foreach (const v; [[1]]) works, but this doesn't (and it probably should):

class Test
{
}

foreach (const v; [new Test()])