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Template question

 
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Robin



Joined: 21 Apr 2004
Posts: 2
PostPosted: Wed Apr 21, 2004 7:47 pm    Post subject: Template question Reply with quote
Is it possible to use templates to set how many and what type of parameters a function should take?

I want to make an EventHandler class which overloads the ~= operator for adding delegates(with parameters specified by template) and the () operator for executing all delegates again taking said parameters.

Here's an example of an un-templateized handler:

class KeyHandler {
public void opCatAssign(void delegate(int key) handler) {
handlers ~= handler;
}

public void opCall(int key) {
for(int i = 0; i < handlers.length; ++i) {
handlers[i](key);
}
}

private void delegate(int key)[] handlers;
}

It would be nice to not have to make a new one for each Handler type.
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Carlos



Joined: 19 Mar 2004
Posts: 396
Location: Canyon, TX
PostPosted: Wed Apr 21, 2004 10:33 pm    Post subject: Re: Template question Reply with quote
Robin wrote:
Is it possible to use templates to set how many and what type of parameters a function should take?

I want to make an EventHandler class which overloads the ~= operator for adding delegates(with parameters specified by template) and the () operator for executing all delegates again taking said parameters.

Here's an example of an un-templateized handler:

class KeyHandler {
public void opCatAssign(void delegate(int key) handler) {
handlers ~= handler;
}

public void opCall(int key) {
for(int i = 0; i < handlers.length; ++i) {
handlers[i](key);
}
}

private void delegate(int key)[] handlers;
}

It would be nice to not have to make a new one for each Handler type.


You can do this:
Code:

class KeyHandler (T) {
   public void opCatAssign(void delegate(T key) handler) {
      handlers ~= handler;
   }

   public void opCall(T key) {
      for(int i = 0; i < handlers.length; ++i) {
         handlers[i](key);
      }
   }

   private void delegate(T key)[] handlers;
}
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Robin



Joined: 21 Apr 2004
Posts: 2
PostPosted: Thu Apr 22, 2004 11:05 am    Post subject: Re: Template question Reply with quote
Carlos wrote:
Robin wrote:
Is it possible to use templates to set how many and what type of parameters a function should take?

I want to make an EventHandler class which overloads the ~= operator for adding delegates(with parameters specified by template) and the () operator for executing all delegates again taking said parameters.

Here's an example of an un-templateized handler:

class KeyHandler {
public void opCatAssign(void delegate(int key) handler) {
handlers ~= handler;
}

public void opCall(int key) {
for(int i = 0; i < handlers.length; ++i) {
handlers[i](key);
}
}

private void delegate(int key)[] handlers;
}

It would be nice to not have to make a new one for each Handler type.


You can do this:
Code:

class KeyHandler (T) {
   public void opCatAssign(void delegate(T key) handler) {
      handlers ~= handler;
   }

   public void opCall(T key) {
      for(int i = 0; i < handlers.length; ++i) {
         handlers[i](key);
      }
   }

   private void delegate(T key)[] handlers;
}


Yes but that would still be just a key handler. What if I want a MouseButtonHandler which takes two arguments, namely x and y?
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Carlos



Joined: 19 Mar 2004
Posts: 396
Location: Canyon, TX
PostPosted: Thu Apr 22, 2004 4:50 pm    Post subject: Re: Template question Reply with quote
Robin wrote:
Yes but that would still be just a key handler. What if I want a MouseButtonHandler which takes two arguments, namely x and y?


First thing that comes to my mind is you can do this:

Code:
class MouseButtonHandler (T,U) {
   public void opCatAssign(void delegate(T,U) handler) {
      handlers ~= handler;
   }

   public void opCall(T x,U y) {
      for(int i = 0; i < handlers.length; ++i) {
         handlers[i](x,y);
      }
   }

   private void delegate(T,U)[] handlers;
}


However, you're probably gonna end up with many types for a template. So what about a suggestion: why don't you go .net like and have a base EventArgs class and have others subclass it. Each subclass would define more attributes for its respective handlers.
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l8night



Joined: 03 May 2004
Posts: 32
Location: UK
PostPosted: Mon May 03, 2004 4:48 pm    Post subject: Reply with quote
you might want to consider this ...
Code:

class HandleArray( H ) {
   protected:
       alias H HandlerType;
      H[] handlers;
      bit findResult( bit delegate(H) predicate ) {
         foreach( HandlerType handler; handlers ) {
            if ( predicate( handler ) ) { return true; }
         }
         return false;
      }
      void onall( void delegate(H) action ) {
         foreach( HandlerType handler; handlers ) {
            action( handler );
         }
      }
   public:
    void opCatAssign( H handler ) {
      handlers ~= handler;
   }
}

class ProcHandler( P ) : HandleArray!( void delegate( P ) ) {
   public void opCall( P p ) {
      onall( delegate void( HandlerType h ) { h(p); } );
   }
}

class ProcHandler( P0, P1 ) : HandleArray!( void delegate(P0, P1) ) {
   public void opCall( P0 p0, P1 p1 ) {
      onall( delegate void( HandlerType h ) { h(p0, p1); } );
   }
}

class FuncHandler( R, P ) : HandleArray!( bit delegate( out R, P ) ) {
   public R opCall( P p ) {
      R rv = R.init;
      findResult( delegate bit( HandlerType h ) { return h( rv, p ); } );
      return rv;
   }
}
///-- example test code;
class IntScanner : FuncHandler!( int, int ) {
}

void test1() {
   IntScanner scan = new IntScanner();
   bit scanFor1( out int rv, int val ) { if ( val == 1 ) { rv = 10; return true; } return false; }
   bit scanFor3( out int rv, int val ) { if ( val == 3 ) { rv = 30; return true; } return false; }
   scan ~= &scanFor1;
   scan ~= &scanFor3;
   for ( int i = 0; i < 4; i++ ) {
      printf( "scan(?d) = ?d\n", i, scan( i ) );
   }
}

void test2() {
   ProcHandler!( int, char[] ) scan;
   scan = new typeof(scan)();
   void show( int val, char[] name ) { printf( "show[?d]:?.*s\n", val, name ); }
   void showagain( int val, char[] name ) { printf( "showagain[?d]:?.*s\n", val, name ); }
   scan ~= &show;
   scan ~= &showagain;
   scan( 1, "one" );
   scan( 2, "two" );
}

int main( char[][] args ) {
   test1();
   test2();
   return 0;
}

whilst you still need a templated class for each number of parameters you need to handle is is a very simple class eg ...
Code:

class ProcHandler( P0, P1, P2 ) : HandleArray!( void delegate(P0, P1,P2) ) {
   public void opCall( P0 p0, P1 p1, P2 p2 ) {
      onall( delegate void( HandlerType h ) { h(p0, p1, p2); } );
   }
}
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Hohums



Joined: 08 Apr 2004
Posts: 71
Location: Western Australia
PostPosted: Mon May 03, 2004 7:21 pm    Post subject: Re: Template question Reply with quote
Robin wrote:


Yes but that would still be just a key handler. What if I want a MouseButtonHandler which takes two arguments, namely x and y?


Just pass the template a struct. ie

class dispatcher(T)
{
....
}

struct mouseEvent
{
int x;
int y;
}

alias dispatcher!(mouseevent) dispatcher;
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