On Friday, 25 October 2019 at 20:44:18 UTC, Dennis wrote:
On Friday, 25 October 2019 at 19:49:05 UTC, Ali Çehreli wrote:
I'm still not completely sold on the whole idea though because
it's not a clear win.
Do others see other advantages in other places like templates?
For example, could templates really be written generically for
arrays and associative arrays?
I'm personally not concerned about generic code.
- The semantics of `in` aren't very well defined anyways.
- Those who write templates like that (hopefully) know what
they're doing, they'll figure it out ;)
- I can't think of situations where you actually want to write
code that generically works on both arrays and associative
arrays like that. (Though if anyone knows one, please share,
I'm interested.)
I'm more concerned about the repeated reports of users being
surprised that `in` doesn't work like they expect. In Python,
the expression `3 in [2, 3, 4]` returns a boolean, and in D you
can do `bool b = 15 in iota(10, 20)` because the operator is
overloaded in Phobos for iota; But as far as actual language
support, `in` is only defined for associative arrays:
https://dlang.org/spec/expression.html#InExpression
It returns a pointer which can be used in an if-statement, but
also to read/modify the value. So should `in` on arrays do the
same? It would be consistent, but usage of raw pointers is
discouraged with the advent of scope and ref etc. Also you
can't implicitly convert a pointer to a boolean.
Should it be a boolean then? That means part of the result of
the linear search is discarded, making `in` less flexible.
So maybe we should leave it for now, and put a small
explanation in the error message.
I'm also not so fond of that "in" operator returns a pointer
which is bad fit for arrays and possibly many other container
algorithms as well. I think the best would be that it would
return an optional of type T and T would be user defined. For
associative arrays, a pointer or a reference to the element. For
arrays the index of that element would suitable. Also overloading
would be nice so that "in" operator could return several possible
optional types, not sure if that would be possible though.
