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digitalmars.D.learn - Partial specialisation: howto? (in the right news group this time.

reply div0 <div0 users.sourceforge.net> writes:
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Hi Everybody,

Please have a look at the appended sucky code.

Obv. the createHandlerCode function is a pain in the back side for
extending this system; I want multiple different partially specialised
implementations.

So whats the syntax for doing partial specialisation?

Damed if I can work it out.

==================

enum EHandlerType {
	eMsgRangeHdlr,
	eMsgHdlr,
	eCmdIdHdlr
}

template createHandlerCode(T ...) {
	string format() {
		static if(T[0]._type == EHandlerType.eMsgRangeHdlr)
			return createMessageRangeHandler!(T).format();
		else static if(T[0]._type == EHandlerType.eMsgHdlr)
			return createMessageHandler!(T).format();
		else static if(T[0]._type == EHandlerType.eCmdIdHdlr)
			return createCommandIdHandler!(T).format();
		else
			static assert(false, "handler type not handled");
	}
}

struct msgRangeHdlr(uint msgIdFirst, uint msgIdLast, string
responseMethod) {
	invariant EHandlerType	_type = EHandlerType.eMsgRangeHdlr;
	invariant string	_msgIdFirst = std.metastrings.ToString!(msgIdFirst);
	invariant string	_msgIdLast = std.metastrings.ToString!(msgIdLast);
	invariant string 	_responseMethod = responseMethod;
}

struct msgHdlr(uint msgId, string responseMethod) {
	invariant EHandlerType	_type = EHandlerType.eMsgHdlr;
	invariant string	_msgId = std.metastrings.ToString!(msgId);
	invariant string 	_responseMethod = responseMethod;
}

struct cmdIdHdlr(uint cmdId, string responseMethod) {
	invariant EHandlerType	_type = EHandlerType.eCmdIdHdlr;
	invariant string	_cmdId = std.metastrings.ToString!(cmdId);
	invariant string 	_responseMethod = responseMethod;
}

- --
My enormous talent is exceeded only by my outrageous laziness.
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May 16 2009
parent reply "Simen Kjaeraas" <simen.kjaras gmail.com> writes:
div0 wrote:

It seems I might know how to do this after all.

As is mentioned under template constraints[1], templates can be specialized by
trailing the parameter list with a condition:

template createHandlerCode( T... ) if ( T[0]._type ==
EHandlerType.eMsgRangeHdlr ) {
  string format( ) {
    return createMessageRangeHandler!( T ).format();
  }
}
template createHandlerCode( T... ) if ( T[0]._type == EHandlerType.eMsgHdlr ) {
  string format( ) {
    return createMessageHandler!( T ).format();
  }
}
template createHandlerCode( T... ) if ( T[0]._type == EHandlerType.eCmdIdHdlr )
{
  string format( ) {
    return createCommandIdHandler!( T ).format();
  }
}

This code is D2-only and untested, so there is certainly a possibility it will
not work for you.

[1]: http://www.digitalmars.com/d/2.0/template.html#Constraint

--
  Simen
May 16 2009
parent reply div0 <div0 users.sourceforge.net> writes:
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Thanks Simen,

That's nicer than the chained static ifs.
Is there anyway to get rid of the enum though?

Using the enum is a pain as it means you have to edit that import
anytime you need to create a specialistion.

Simen Kjaeraas wrote:

 div0 wrote:
 
 It seems I might know how to do this after all.
 
 As is mentioned under template constraints[1], templates can be
 specialized by trailing the parameter list with a condition:
 
 template createHandlerCode( T... ) if ( T[0]._type ==
 EHandlerType.eMsgRangeHdlr ) {
  string format( ) {
    return createMessageRangeHandler!( T ).format();
  }
 }
 template createHandlerCode( T... ) if ( T[0]._type ==
 EHandlerType.eMsgHdlr ) {
  string format( ) {
    return createMessageHandler!( T ).format();
  }
 }
 template createHandlerCode( T... ) if ( T[0]._type ==
 EHandlerType.eCmdIdHdlr ) {
  string format( ) {
    return createCommandIdHandler!( T ).format();
  }
 }
 
 This code is D2-only and untested, so there is certainly a possibility
 it will not work for you.
 
 [1]: http://www.digitalmars.com/d/2.0/template.html#Constraint
 
 -- 
  Simen



- --
My enormous talent is exceeded only by my outrageous laziness.
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May 17 2009
next sibling parent reply Jason House <jason.james.house gmail.com> writes:
div0 wrote:


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 Thanks Simen,
 
 That's nicer than the chained static ifs.
 Is there anyway to get rid of the enum though?
 
 Using the enum is a pain as it means you have to edit that import
 anytime you need to create a specialistion.


It's nearly impossible to answer your question without knowing what you're 
trying to achieve.  For example, you're specializing on T... which means 
there are more template arguments.  Is there anything differentiating the 
cases in those?  Another candidate is a class hierarchy (or use of an 
interface) where createHandlerCode is defined in the base definition, and 
each inheriting class overrides the method.
May 17 2009
parent div0 <div0 users.sourceforge.net> writes:
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Jason House wrote:

 div0 wrote:
 

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 Hash: SHA1

 Thanks Simen,

 That's nicer than the chained static ifs.
 Is there anyway to get rid of the enum though?

 Using the enum is a pain as it means you have to edit that import
 anytime you need to create a specialistion.


 
 It's nearly impossible to answer your question without knowing what you're 
 trying to achieve.  For example, you're specializing on T... which means 
 there are more template arguments.  Is there anything differentiating the 
 cases in those?  Another candidate is a class hierarchy (or use of an 
 interface) where createHandlerCode is defined in the base definition, and 
 each inheriting class overrides the method.
 


I've just reread it and realised I deleted too much stuff for anybody to
get what I was after. doh.

But as per usual, I thought of a much easier way to do it about 10
minutes after I asked the question.

Thanks for your responses though! :)

- --
My enormous talent is exceeded only by my outrageous laziness.
http://www.ssTk.co.uk
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May 17 2009
prev sibling parent "Simen Kjaeraas" <simen.kjaras gmail.com> writes:
div0 wrote:


 Thanks Simen,

 That's nicer than the chained static ifs.
 Is there anyway to get rid of the enum though?


I would believe this to work:


template createHandlerCode( T... ) if ( is( T == msgRangeHdlr ) ) {
	string format( ) {
		return createMessageRangeHandler!(T).format();
	}
}
template createHandlerCode( T... ) if ( is( T == msgHdlr ) ) {
	string format( ) {
		return createMessageHandler!(T).format();
	}
}
template createHandlerCode( T... ) if ( is( T == cmdIdHdlr ) ) {
	string format( ) {
		return createCommandIdHandler!(T).format();
	}
}

--
  Simen
May 17 2009