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digitalmars.D - Extracting function param types using variadic templates

reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
Hmm.

I can do this:

void variadic(T...)(T args){}
variadic(1, 2, 3);

This:

void returnType(T)(T delegate() dg){}

returnType(delegate int(){ return 0; });

Even this:

void returnAndArg(T, U)(T delegate(U) dg){}
returnAndArg(delegate int(bool b){ return 0; });

But not:

void returnAndArgs(T, U...)(T delegate(U) dg){}
returnAndArgs(delegate int(bool b){ return 0; });

!

One can dream, no?

Is there maybe some other way to get at the parameter types of a function as 
a tuple, using variadic magic?
Nov 03 2006
parent reply Tom S <h3r3tic remove.mat.uni.torun.pl> writes:
Jarrett Billingsley wrote:

 Is there maybe some other way to get at the parameter types of a function as 
 a tuple, using variadic magic? 



How about this stuff: 
http://www.dsource.org/projects/pyd/browser/trunk/infrastructure/meta ?
Nov 03 2006
parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Tom S" <h3r3tic remove.mat.uni.torun.pl> wrote in message 
news:eigch3$ilf$1 digitaldaemon.com...

 Jarrett Billingsley wrote:

 Is there maybe some other way to get at the parameter types of a function 
 as a tuple, using variadic magic?



 How about this stuff: 
 http://www.dsource.org/projects/pyd/browser/trunk/infrastructure/meta ?



But that's basically using my third example, i.e.

void returnAndArg(T, U)(T delegate(U) dg){}
returnAndArg(delegate int(bool b){ return 0; });

But with many specializations of the template, one for each number of 
params.  The point of using variadic templates is removing the need to 
manually create a specialization for each number of things you want in the 
typelist.  With the automatic tuple deduction that I wish existed, the 
FuncMeta.d module would become about 80 lines of code, and it would be able 
to support any number of arguments.
Nov 03 2006
parent reply Kirk McDonald <kirklin.mcdonald gmail.com> writes:
Jarrett Billingsley wrote:

 "Tom S" <h3r3tic remove.mat.uni.torun.pl> wrote in message 
 news:eigch3$ilf$1 digitaldaemon.com...

 Jarrett Billingsley wrote:

 Is there maybe some other way to get at the parameter types of a function 
 as a tuple, using variadic magic?



 http://www.dsource.org/projects/pyd/browser/trunk/infrastructure/meta ?



 But that's basically using my third example, i.e.
 
 void returnAndArg(T, U)(T delegate(U) dg){}
 returnAndArg(delegate int(bool b){ return 0; });
 
 But with many specializations of the template, one for each number of 
 params.  The point of using variadic templates is removing the need to 
 manually create a specialization for each number of things you want in the 
 typelist.  With the automatic tuple deduction that I wish existed, the 
 FuncMeta.d module would become about 80 lines of code, and it would be able 
 to support any number of arguments. 
 
 



This was approximately the first thing I tried doing with variadic 
templates. I was very saddened to see that it doesn't work.

-- 
Kirk McDonald
Pyd: Wrapping Python with D
http://pyd.dsource.org
Nov 03 2006
parent Walter Bright <newshound digitalmars.com> writes:
Kirk McDonald wrote:

 This was approximately the first thing I tried doing with variadic 
 templates. I was very saddened to see that it doesn't work.



I agree, and I'll break out the hammer & tongs and see if I can make it 
work.
Nov 03 2006