Optimize count with an overload which calls walkLength

[RazvanN7]

Following the discussion in #5545 , I created this separate PR for the count optimization. The implementation uses walkLength to compute the count. If walkLength will be deprecated, then I will replace the call with the code, otherwise we can close the other PR and keep just this oprimization

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[UplinkCoder]

Why is that needed.

The ddoc is bigger then the function ?
which is a thunk.
a templated thunk no less.
introducing symbol bloat.
You could just have made an alias you know ...

[RazvanN7]

@UplinkCoder That was the consensus reached in #5545. I guess creating an alias might be better, still the documentation needs to be there

[wilzbach]

You could just have made an alias you know ...

Would break code, due to the different default behavior. count allows a user-defined pred, walkLength allows a maximal count.
Though imho on the long run on of these functions should be deprecated (or at least removed from the docs).

The ddoc is bigger then the function ?

Because documentation is a lot more important than code. This is a common pattern in Phobos ;-)

[RazvanN7]

@wilzbach I created an overload anyway so making an alias won't break any code, but it seems cleaner to me to have an overload, rather then an alias.

[wilzbach]

LGTM to me in general. If we decide to deprecate on of the symbols we can always do this afterwards as this is just an optimization.

[wilzbach]

(keeping this open for one or two days to give people enough time to veto this approach as a general good practice)

[andralex]

length in code font (e.g. backticks)

[andralex]

Aliases are generally better, but here we have overloading so that wouldn't work well.

This improves the situation whereby someone calls count with the default predicate - avoid the goofy walking the whole range. That's fine, as is to allow two distinct library functions sometimes do the same thing under certain circumstances.

[RazvanN7]

@andralex done