www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - An Impressive Feature Without Doc

reply Wei Li <oldrev gmail.com> writes:
Just a moment ago, I met a cool feature but where is the specs for it?

template Floats(T) {
	static if(is(T : real)) {
		alias T Floats;
	}
}

T min(T=Floats)(T x, T y)  // Why we can write T=Floats instead of T=Floats!(T)
?
{
	return x < y ? x : y;
}

Regards
Nov 13 2007
next sibling parent Wei Li <oldrev gmail.com> writes:
Wei Li Wrote:


 Just a moment ago, I met a cool feature but where is the specs for it?
 
 template Floats(T) {
 	static if(is(T : real)) {
 		alias T Floats;
 	}
 }
 
 T min(T=Floats)(T x, T y)  // Why we can write T=Floats instead of
T=Floats!(T) ?
 {
 	return x < y ? x : y;
 }
 
 Regards


Sorry, my fault. I'm confused it with ':'.

Regards
Nov 13 2007
prev sibling parent reply downs <default_357-line yahoo.de> writes:
Wei Li wrote:

 Just a moment ago, I met a cool feature but where is the specs for it?
 
 template Floats(T) {
 	static if(is(T : real)) {
 		alias T Floats;
 	}
 }
 
 T min(T=Floats)(T x, T y)  // Why we can write T=Floats instead of
T=Floats!(T) ?
 {
 	return x < y ? x : y;
 }
 
 Regards


This is one of D's template pitfalls; since min is never instantiated, it
never actually checks if Floats is a valid thing to instantiate min with.
(it's not; a template is not a type).
You can see this by writing


 void main() {
   auto fp=&min!();
 }


which will make the compiler notice the error and barf.
Thanks to KMD for pointing this out.
Nov 14 2007
parent Wei Li <oldrev gmail.com> writes:
downs Wrote:


 Wei Li wrote:

 Just a moment ago, I met a cool feature but where is the specs for it?
 
 template Floats(T) {
 	static if(is(T : real)) {
 		alias T Floats;
 	}
 }
 
 T min(T=Floats)(T x, T y)  // Why we can write T=Floats instead of
T=Floats!(T) ?
 {
 	return x < y ? x : y;
 }
 
 Regards


 
 This is one of D's template pitfalls; since min is never instantiated, it
 never actually checks if Floats is a valid thing to instantiate min with.
 (it's not; a template is not a type).
 You can see this by writing
 

 void main() {
   auto fp=&min!();
 }


 
 which will make the compiler notice the error and barf.
 Thanks to KMD for pointing this out.


I got it, thanks for your explain.

Regards,
Nov 14 2007