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digitalmars.D.learn - limiting templates

reply BCS <ao pathlink.com> writes:
I have a template

int Foo(T)(T bar);

I want to be able to call it like this:

foo("hello");

and have T end up as char[] not char[5]. Is there any way to limit the template 
to that?
May 01 2007
parent reply Daniel Keep <daniel.keep.lists gmail.com> writes:
BCS wrote:
 I have a template
 
 int Foo(T)(T bar);
 
 I want to be able to call it like this:
 
 foo("hello");
 
 and have T end up as char[] not char[5]. Is there any way to limit the
 template to that?

Not one that I can think of off the top of my head. The problem is that you can't specialise templated functions. That said, you might be able to do something like this (note: untested, off the top of my head code): template Foo(T) { static if( IsStaticArray!(T) ) alias Foo!(DynamicArrayFromStaticArray!(T)) Foo; else int Foo(T bar) { ... } } Obviously, you'd have to write IsStaticArray and DynamicArrayFromStaticArray (unless they're in std.traits). The other thing you can do is ensure the argument is really a char[] in the first place: foo("hello"[]); The [] does a slice of the char[5], which results in a char[]. -- Daniel -- int getRandomNumber() { return 4; // chosen by fair dice roll. // guaranteed to be random. } http://xkcd.com/ v2sw5+8Yhw5ln4+5pr6OFPma8u6+7Lw4Tm6+7l6+7D i28a2Xs3MSr2e4/6+7t4TNSMb6HTOp5en5g6RAHCP http://hackerkey.com/
May 01 2007
parent BCS <ao pathlink.com> writes:
Reply to Daniel,

 BCS wrote:
 
 I have a template
 
 int Foo(T)(T bar);
 
 I want to be able to call it like this:
 
 foo("hello");
 
 and have T end up as char[] not char[5]. Is there any way to limit
 the template to that?
 

that you can't specialise templated functions.

Am I not understanding you correctly, I thought this worked (it did the last time I checked) int bar(char[] s: "hello")() { return s.length; } I though of that, but what I going for is code folding to reduce duplication. I just though of what to do int FooT(T)(T bar); alias FooT!(char[]) Foo; alias FooT!(int) Foo; this works because I have a finite list of type that are to be allowed. The "good" way to do it would be to allow for limiting rules to be applied: int foo(T : is(T[]) || !is(T.length)]) ;
May 01 2007