T[] opIndex() Error: .. signal 11

[Paul Backus]

On Tuesday, 3 October 2023 at 17:05:46 UTC, Steven Schveighoffer 
wrote:
> ```d
> void main()
> {
> 	S s = 0;
> 	{
> 		scope int[] __r3 = s.opIndex()[];
> 		ulong __key4 = 0LU;
> 		for (; __key4 < __r3.length; __key4 += 1LU)
> 		{
> 			int x = __r3[__key4];
> 		}
> 	}
> 	return 0;
> }
> ```
>
> Note the difference in how the foreach code is lowered. Inside 
> `opIndex`, it's lowered to the range functions. Outside, it 
> uses the slice operator to switch to iterating a `scope int[]`.

Naturally, this lowering is completely absent from [the language 
spec's section on `foreach`.][1] According to the spec, the only 
ways to iterate over a `struct` type are `opApply` and the input 
range interface.

I think it would probably be less confusing to have both 
`opApply` and `empty`/`front`/`popFront` take precedence over 
this lowering, but I have no idea how much existing code would be 
broken by such a change. At the very least, though, this needs to 
be documented.

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