importing std.algorithm breaks std.string.count

[Steven Schveighoffer]

On Fri, 17 Sep 2010 17:15:31 -0400, Seth Hoenig <seth.a.hoenig at gmail.com>  
wrote:

> I have these two minimal programs:
>
>
> import std.string;
> void main()
> {
>     string str = "abc";
>     int i = str.count("ab");
>
> }
>
>
>
> and:
>
>
>
> import std.string;
> import std.algorithm;
> void main()
> {
>     string str = "abc";
>     int i = str.count("ab");
>
> }
>
>
>
> The only difference is line 2, where I import std.algorithm.
> The first program compiles fine, but the second program does not compile,
> spitting out the error message:
>
> bash-3.2$ dmd -ofdummy dummy.d
> /u/sah2659/dmd2/linux/bin/../../src/phobos/std/functional.d(176): Error:
> static assert  "Bad binary function q{a == b}. You need to use a valid D
> expression using symbols a of type dchar and b of type string."
> /u/sah2659/dmd2/linux/bin/../../src/phobos/std/functional.d(179):
> instantiated from here: Body!(dchar,string)
> /u/sah2659/dmd2/linux/bin/../../src/phobos/std/algorithm.d(3410):
> instantiated from here: result!(dchar,string)
> dummy.d(7):        instantiated from here: count!("a == b",string,string)
>
>
> I can't imagine I'm the first person to notice a bug like this, so is  
> there
> something I am doing wrong?

I see two bugs here.  First, this should be an ambiguity error, because  
count matches both std.algorithm.count and std.string.count.  The compiler  
should refuse to compile this I think.

Second, std.algorithm.count looks like this:

size_t count(alias pred = "a == b", Range, E)(Range r, E value) if  
(isInputRange!(Range))

So, E can be any type, completely unrelated to strings, I could do:

count!(string, int[]) which makes no sense.

I think the sig should be

size_t count(alias pred = "a == b", Range, E)(Range r, E value) if  
(isInputRange!(Range) && isImplicitlyConvertable!(E, ElementType!(Range)))

-Steve