Michel Fortin wrote:
> On 2011-02-01 10:34:26 -0500, Andrei Alexandrescu
> <[email protected]> said:
>
> >On 2/1/11 9:21 AM, Don wrote:
> >>Jonathan M Davis wrote:
> >>>Do you really find
> >>>
> >>>assertPred!"=="(min(5, 7), 5);
> >>>
> >>>to be all that harder to understand than
> >>>
> >>>assert(min(5, 7) == 5);
> >>
> >>I do. *Much* harder. Factor of two, at least.
> >>In absolute terms, not so much, because it was the original assert is
> >>very easy to understand. But the relative factor matters enormously.
> >>Much as comparing:
> >>a.add(b);
> >>a += b;
> >>
> >>And I think this is a very important issue.
> >>
> >> >I don't see how these functions could be anything but an improvement.
> >> > But even if they get into Phobos, you obviously don't have to use them.
> >>
> >>This is not true. Including them in Phobos gives a legitimacy to that
> >>style of programming. It's a role model.
> >>
> >>Including stuff like this could give D a reputation for lack of
> >>readability. My belief is that right now, the #1 risk for Phobos is that
> >>it becomes too clever and inaccessible.
> >>
> >>IMHO, something simple which has any appearance of being complicated,
> >>needs a VERY strong justification.
> >
> >Does this count as a vote against the submission?
>
> To me this is a compelling argument against. That and the fact that
> it can't really mimic the true behaviour of assert in some
> situation. assertPred won't work correctly for 'in' contracts with
> inheritance, where the compiler generate the assertion code
> differently.
>
> In my view, the correct way to improve assertion error messages is
> to improve how the compiler handle assertions (it should output
> messages like it does for static asserts).
>
> assertPred might be fine as a stopgap solution, but personally I'd
> not make it part of the public API. We can't tell people to use
> assert() everywhere and then tell them they should use
> assertPred!op() if they want a useful error message except for 'in'
> contracts of virtual functions; that'd just be too confusing.
Actually we say use assertPred/etc. when writing unittests, don't we? To
me that is not complicated. There used to be a version(unittest). I
don't know for what reason it got removed. If it was still there an else
could help a bit. Like
version(unittest) {
}
else {
static assert(false, "assertPred/etc. are only available within
unittests.");
}
Now every code compiled without -unittest and using assertPred/etc will
fail to compile. But of course with -unittest it still seems that it
will work in contracts. I mean at least we can make the problem explicit
in most cases. Not sure how likely it is that people will distribute
software that they only compiled with unittests.
Jens
