TDPL: Overloading template functions

[Philippe Sigaud]

On Wed, Jul 28, 2010 at 05:50, Andrej Mitrovic
<andrej.mitrovich at gmail.com>wrote:

I won't comment on the double/float issue, I do not anything about it.


> T[] find(T, E)(T[] haystack, E needle)
>    if (is(typeof(haystack[0] != needle) == bool))
>
> T1[] find(T1, T2)(T1[] longer, T2[] shorter)
>    if (is(typeof(longer[0 .. 1] == shorter) : bool))
>
> Also, Andrei, you never explained the if(is()) signature of the second
> templated function. I hope to get some pointers on that. :)
>

I'll have a try at this one.
As you may know, the is(typeof()) syntax is a way to try to compile an
expression and see if it works. If it works, it has a type, given by typeof
and is(Type) returns true. So the first one is really saying: "Hey compiler,
may I compare an element of haystack (of type T) with an E
In this case, longer is an array. So longer[0] would be an element, a T1.
There is no chance that shorter will match as an element cannot be equal to
an array ... except, of course, if longer is an array of T2[]  (T1 == T2[]).
Longer is a T2[][]. That may happen for arrays of strings, strings being
arrays of chars. And I think that's the problem you have in your last unit
test.

Anyway, he takes longer[0..1] to get a slice, which is a dynamic array, a
T1[] and hence comparable to a T2[]... most of the time.

As for using ': bool' instead of '== bool' as in the first find(),  I don't
think there is any difference in this case. I understand T == U as 'T is the
exact same type as U', whereas T : U is for me "T is a subtype of U". But
then, a subtype of bool is pretty much constrained to be a bool. The T : U
syntax is pretty much only used for classes : if(is(T : MyClass)) is saying
: 'compile this only if T is a subclass of MyClass'.


Philippe



, except if longer is in fact
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