• Reiner Pope (7/7) Jul 16 2006 When making a program with a callback, how do you decide whether to use
• Kirk McDonald (13/23) Jul 17 2006 Delegates are functions with context. They are therefore more useful in
• Reiner Pope (3/25) Jul 17 2006 Thanks for the response. I thought that was the case, but I didn't
• Lionello Lunesu (7/9) Jul 18 2006 For extern (C) functions that only want a function pointer, like qsort's...
• Chris Nicholson-Sauls (24/34) Jul 17 2006 I would say, when in doubt, go with delegate. Why? Consider usage exam...
• Reiner Pope (2/11) Jul 17 2006 Is it really necessary to *wrap* it? I'm surprised there isn't a cast to...
• Don Clugston (4/15) Jul 17 2006 The calling convention is actually different, you need to create a
• Walter Bright (3/5) Jul 22 2006 The only way to do it is to generate a "thunk" of executable code at
• Chad J (5/15) Jul 17 2006 I started a thread along these lines not too long ago, and it had some

Reiner Pope <reiner.pope gmail.com> writes:

When making a program with a callback, how do you decide whether to use 
a function or a delegate? E.g,

   void foo(void function(int) consume)
   { ... }

or

   void foo(void delegate(int) consume)
   { ... }

Kirk McDonald <kirklin.mcdonald gmail.com> writes:

Reiner Pope wrote:
 When making a program with a callback, how do you decide whether to use 
 a function or a delegate? E.g,
 
   void foo(void function(int) consume)
   { ... }
 
 or
 
   void foo(void delegate(int) consume)
   { ... }

Delegates are functions with context. They are therefore more useful in 
the general case. (It is easier to turn a function into a delegate than 
vice-versa.) However, which one you want depends on your use-case. When 
in doubt, I would default to using a delegate. This allows the use of 
lambda functions as callbacks, if nothing else.

Walter has said on a number of occasions that he eventually (as in, 2.0) 
wants to make function pointers and delegates the same thing, which will 
make the question moot.

-- 
Kirk McDonald
Pyd: Wrapping Python with D
http://dsource.org/projects/pyd/wiki

Reiner Pope <reiner.pope gmail.com> writes:

Kirk McDonald wrote:
 Reiner Pope wrote:
 When making a program with a callback, how do you decide whether to 
 use a function or a delegate? E.g,

   void foo(void function(int) consume)
   { ... }

 or

   void foo(void delegate(int) consume)
   { ... }

 
 Delegates are functions with context. They are therefore more useful in 
 the general case. (It is easier to turn a function into a delegate than 
 vice-versa.) However, which one you want depends on your use-case. When 
 in doubt, I would default to using a delegate. This allows the use of 
 lambda functions as callbacks, if nothing else.
 
 Walter has said on a number of occasions that he eventually (as in, 2.0) 
 wants to make function pointers and delegates the same thing, which will 
 make the question moot.
 

Thanks for the response. I thought that was the case, but I didn't 
really see why functions would really be in the spec in that case.

Lionello Lunesu <lio lunesu.remove.com> writes:

Reiner Pope wrote:
 Thanks for the response. I thought that was the case, but I didn't 
 really see why functions would really be in the spec in that case.

For extern (C) functions that only want a function pointer, like qsort's 
int (*compare)(void*,void*)

L.

Notice that you can easily wrap a function to pass it as a delegate, 
using the new function literal syntax. There's another post in this 
group explaining it in more detail.

Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:

Reiner Pope wrote:
 When making a program with a callback, how do you decide whether to use 
 a function or a delegate? E.g,
 
   void foo(void function(int) consume)
   { ... }
 
 or
 
   void foo(void delegate(int) consume)
   { ... }

I would say, when in doubt, go with delegate.  Why?  Consider usage examples of
your 
foo()'s signature:




Simple!  If you made it a function pointer, then (as far as I know) using
member functions 
and nested functions (which would be done the same way as above, just without
'obj') 
ceases to be possible at all.  (If there is a hack or workaround to pass a
delegate as a 
function pointer, I want to see that!)







Concise!  The utility of this should be fairly self-explanatory.



anonymous delegate:








Intuitive?  Maybe not; but still quite straight-forward.

-- Chris Nicholson-Sauls

Reiner Pope <reiner.pope gmail.com> writes:

 anonymous delegate:








Is it really necessary to *wrap* it? I'm surprised there isn't a cast to 
do it.

Don Clugston <dac nospam.com.au> writes:

Reiner Pope wrote:

 an anonymous delegate:








 Is it really necessary to *wrap* it? I'm surprised there isn't a cast to 
 do it.

The calling convention is actually different, you need to create a 
'thunk' to convert function to delegate. The compiler doesn't do this 
for you yet.

Walter Bright <newshound digitalmars.com> writes:

Chris Nicholson-Sauls wrote:
 (If there is a hack or workaround to pass a delegate as a function 
 pointer, I want to see that!)

The only way to do it is to generate a "thunk" of executable code at 
runtime.

Chad J <gamerChad _spamIsBad_gmail.com> writes:

Reiner Pope wrote:
 When making a program with a callback, how do you decide whether to use 
 a function or a delegate? E.g,
 
   void foo(void function(int) consume)
   { ... }
 
 or
 
   void foo(void delegate(int) consume)
   { ... }

I started a thread along these lines not too long ago, and it had some 
good responses.

Here it is:
http://www.digitalmars.com/drn-bin/wwwnews?digitalmars.D.learn/3700