• js.mdnq (24/24) Nov 29 2012 I need to store a templated function in a function pointer, how
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (26/33) Nov 29 2012 std.functional may have something:
• js.mdnq (7/7) Nov 30 2012 It seems one can accomplish this using delegates assigned by
• bearophile (7/9) Nov 30 2012 If you care so much for performance, when you work with D

"js.mdnq" <js_adddot+mdng gmail.com> writes:

I need to store a templated function in a function pointer, how 
can I do this?


e.g.,

void function(double) myfuncptr;
void myfunc(double d) { }
myfuncptr = myfunc;

Now I would like to use a template parameter instead of double.

In C++ one can do this by using boosts binding's and function 
types.

For example, I want something like this

void function(F)(F) funcptr;

void Bind(T)(void function(T)(T) v)
{
     funcptr = v; // F is sort of deduced automatically as being 
T. Obviously problematic but effectively what I want to do.
}

This way I can bind to any function that takes a single type 
parameter and returns a void.


void function(F) myfuncptr;  // F is undefined
void myfunc(T)(T d) { }      //
myfuncptr = myfunc;

To do this using boost I would simply bind the parameter so 
myfuncptr would not depend on an arbitrary type.

I need a rather performant way to do this too.

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 11/29/2012 03:17 PM, js.mdnq wrote:
 I need to store a templated function in a function pointer, how can I do
 this?


 e.g.,

 void function(double) myfuncptr;
 void myfunc(double d) { }
 myfuncptr = myfunc;

 Now I would like to use a template parameter instead of double.

std.functional may have something:

   http://dlang.org/phobos/std_functional.html

Are you looking for something like the following?

import std.traits;

auto myDelegate(F : T function(T), T)(F f)
     if (isFunctionPointer!F)  // <-- probably unnecessary
{
     return (T a) => f(a * 2);
}

double func_double(double d)
{
     return d;
}

int func_int(int i)
{
     return i;
}

void main()
{
     auto d = myDelegate(&func_double);
     auto i = myDelegate(&func_int);

     assert(d(1.5) == 3.0);
     assert(i(42) == 84);
}

Ali

"js.mdnq" <js_adddot+mdng gmail.com> writes:

It seems one can accomplish this using delegates assigned by 
generic functions. The delegate will end hold holding the "state" 
of the function. It sort of acts like a binder. It seems to work 
but more testing needs to be done. I'm not sure how efficient it 
is or if there is a better way but basically it seems rather 
elegant(rather than trying to create some new type to deal with 
it).

"bearophile" <bearophileHUGS lycos.com> writes:

js.mdnq:

 It seems one can accomplish this using delegates assigned by 
 generic functions.

If you care so much for performance, when you work with D 
delegates it's useful to know the difference between static/scope 
delegates (that are just a fat pointer) and closures (that often 
induce a heap allocation).

Bye,
bearophile