More bugs...

[Timon Gehr]

On 05/01/2012 01:20 PM, Mehrdad wrote:
> I guess the problem is with type deduction, but the trouble is that half
> the reason why type deduction is useful is in the case of lambdas. They
> become effectively useless if you have to type out their entire
> signature, since you could then just make them a separate function (or
> just use a mixin instead, to create a closure... which I've done before).
>
> This isn't really an 'enhancement', since the error message is clearly a
> bug. So I filed them both as bugs.
>
> http://d.puremagic.com/issues/show_bug.cgi?id=8009
> http://d.puremagic.com/issues/show_bug.cgi?id=8010
>
> The other bug I was referring to was something along the lines of the
> compiler telling me, "I can't really handle closures as template
> parameters very well (something about 'local variable' or whatever), so
> I'll just give you an obscure error every now and then".
> It only happened when it was inside another function, and some
> conditions were satisfied. (I don't remember the exact message, but when
> I searched it, I saw it had been already reported before...)
>

Probably you mean this one:

struct S{
     int x;
     auto foo(alias a)(){return a(x);}
}

void main(){
     auto s = S(2);
     int y = 3;
     writeln(s.foo!(x=>x+y)());
}

Error: template instance foo!(__lambda2) cannot use local 
'__lambda2(__T1)' as parameter to non-global template foo(alias a)

This is an arbitrary restriction and should be fixed. The 'this' pointer 
for 'foo' could be passed in a reserved slot at the beginning of the 
context for 'main'.


>
> Oh and thanks for the alternative, it's a good workaround to know. :)
>
> The trouble is that while it solves the bug I posted, it's still not
> solving my (actual) problem.
> The actual problem was that I wanted to do something along the lines of:
>
> private import std.range;
> auto filter(R, F)(R r, F f) { /*return a filtered range*/ }
> void main() { [1, 2, 3].filter(x => x < 3); }
>

private import std.range;
auto filter(R, F)(R r, F f) { /*return a filtered range*/ }
void main() { [1, 2, 3].filter((int x) => x < 3); }