https://issues.dlang.org/show_bug.cgi?id=13683

Nick Treleaven <nick@geany.org> changed:

           What    |Removed                     |Added
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           See Also|                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=23663

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https://issues.dlang.org/show_bug.cgi?id=13683

--- Comment #5 from Nick Treleaven <nick@geany.org> ---
static assert is an improvement over the constraint, but it still hides the actual error message which should be:

Error: use `!is` instead of `!=` when comparing with `null`

Removing the constraint allows the correct error to be seen. But then the constraint may be needed to disambiguate overloads. Without a compiler solution,  we could have a new trait - __traits(canPass, pred, range.front) which ignores the body of pred:

https://forum.dlang.org/post/lekofsbnstkoqpspramg@forum.dlang.org

In the absence of that, the best I've come up with is:

if (__traits(isTemplate, pred) || is(typeof(pred(range.front))))

Which doesn't check that pred can take that argument when pred is a lambda, but it doesn't hide the actual error unlike the constraint status quo or the static assert way.

A compiler solution might not work in the presence of overloads, because currently failing constraints are only shown when there are no overloads.

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https://issues.dlang.org/show_bug.cgi?id=13683

--- Comment #6 from Nick Treleaven <nick@geany.org> ---
> Without a compiler solution

BTW that would show the failing lambda with Phobos as is. The static assert PR discussion said a compiler solution is needed rather than having to update every template that accepts a lambda in Phobos.

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