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digitalmars.D.learn - strange template syntax

reply Philippe Sigaud <philippe.sigaud gmail.com> writes:
Hello,

some time ago, chris (ruunhb) posted something on his Dspec project, where he
used a template syntax I didn't know:

----
void each(alias array, T : T[] = typeof(array))(void delegate(T item) dg) {
 foreach(T i; array)
   dg(i);
}

 int[] array = [1, 2, 3, 4];
 int b = 10;

 each!(array) = (int item) {
   writefln("%d", item + b);
 };
---

I'm intrigued by the last lines. I'd have thought 'each' to be invoked by:

each!(array)( (int item) {writefln("%d", item+b)} );

But this doesn't work. And I never encountered Chris' syntax before:

template!(someArgs) = moreArgs;

Could some be nice enough to enlighten me? How does that work?


Philippe
Apr 11 2010
next sibling parent reply Robert Clipsham <robert octarineparrot.com> writes:
On 11/04/10 15:48, Philippe Sigaud wrote:

 Hello,

 some time ago, chris (ruunhb) posted something on his Dspec project, where he
 used a template syntax I didn't know:

 ----
 void each(alias array, T : T[] = typeof(array))(void delegate(T item) dg) {
   foreach(T i; array)
     dg(i);
 }

   int[] array = [1, 2, 3, 4];
   int b = 10;

   each!(array) = (int item) {
     writefln("%d", item + b);
   };
 ---

 I'm intrigued by the last lines. I'd have thought 'each' to be invoked by:

 each!(array)( (int item) {writefln("%d", item+b)} );

 But this doesn't work. And I never encountered Chris' syntax before:

 template!(someArgs) = moreArgs;

 Could some be nice enough to enlighten me? How does that work?


 Philippe


When using your method, you have to use:
----
each!(array, typeof(array))((int item) {writefln("%d", item+b)});
----
(I believe this is a bug, dmd should be able to deduce the type here). 
As for the syntax, you can do this with any function in D:
----
void foo(int a) { writefln( "%d", a ); }
/// Prints 1
foo = 1;
----
I didn't realize this worked for free functions, apparently it does. I 
think in newer versions of D2 functions like this will have to be marked 
with  property, I don't think dmd currently enforces this though.
Apr 11 2010
next sibling parent Philippe Sigaud <philippe.sigaud gmail.com> writes:
On Sun, Apr 11, 2010 at 17:01, Robert Clipsham <robert octarineparrot.com>wrote:


 When using your method, you have to use:
 ----
 each!(array, typeof(array))((int item) {writefln("%d", item+b)});
 ----
 (I believe this is a bug, dmd should be able to deduce the type here).



OK.  I suppose I'd do:

void each(alias array)(void delegate(ElementType!(typeof(array)) item) dg)
if (isArray!(typeof(array))) {
 foreach(T i; array)
  dg(i);
}

and then:

each!([0,1,2,3])(
    (int i) { writeln(i);}
);





 As for the syntax, you can do this with any function in D:
 ----
 void foo(int a) { writefln( "%d", a ); }
 /// Prints 1
 foo = 1;
 ----
 I didn't realize this worked for free functions, apparently it does. I
 think in newer versions of D2 functions like this will have to be marked
 with  property, I don't think dmd currently enforces this though.


Urgh. OK, I didn't think of properties, thanks a lot Robert !
I think it explains some strange errors I have somewhere else, when trying
to assign some value and getting strange unvalid args errors. DMD transforms
my foo = something into foo(something).
Apr 11 2010
prev sibling parent Robert Clipsham <robert octarineparrot.com> writes:
On 11/04/10 16:01, Robert Clipsham wrote:

 When using your method, you have to use:
 ----
 each!(array, typeof(array))((int item) {writefln("%d", item+b)});
 ----
 (I believe this is a bug, dmd should be able to deduce the type here).
 As for the syntax, you can do this with any function in D:
 ----
 void foo(int a) { writefln( "%d", a ); }
 /// Prints 1
 foo = 1;
 ----
 I didn't realize this worked for free functions, apparently it does. I
 think in newer versions of D2 functions like this will have to be marked
 with  property, I don't think dmd currently enforces this though.


When I tried again, your method worked... odd, I must have done 
something wrong before.
Apr 11 2010
prev sibling parent BCS <none anon.com> writes:
Hello Philippe,


 Hello,
 
 some time ago, chris (ruunhb) posted something on his Dspec project,
 where he used a template syntax I didn't know:
 
 ----
 void each(alias array, T : T[] = typeof(array))(void delegate(T item)
 dg) {
 foreach(T i; array)
 dg(i);
 }
 int[] array = [1, 2, 3, 4];
 int b = 10;
 each!(array) = (int item) {
 writefln("%d", item + b);
 };
 ---
 I'm intrigued by the last lines. I'd have thought 'each' to be invoked
 by:
 
 each!(array)( (int item) {writefln("%d", item+b)} );
 


What that is, is the property syntax. I places where there is a function 
named foo that takes one arg, it can be called by "foo = arg;"


 But this doesn't work. And I never encountered Chris' syntax before:


I'm not sure why the normal syntax wouldn't work.

-- 
... <IXOYE><
Apr 11 2010