• Paul D Anderson (40/40) Jun 24 2015 I'm trying to pass a function pointer while keeping the default
• tcak (4/7) Jun 25 2015 I filed a bug about 2-3 months ago about default parameters
• Paul D Anderson (2/11) Jun 25 2015 Thanks
• Paul D Anderson (3/15) Jun 26 2015 Turns out this is expected behavior. Default parameter values are

"Paul D Anderson" <nobody nowhere.none> writes:

I'm trying to pass a function pointer while keeping the default 
parameter values intact. Given the following:

import std.traits;
import std.stdio;

int foo(int a, int b = 1)
{
   return a;
}

alias FOOP = int function(int, int = 1);

struct ST(POOF)
{
   FOOP fctn;

   this(POOF fctn)
   {
     this.fctn = fctn;
   }

   void details()
   {
     alias PDVA = ParameterDefaultValueTuple!fctn;
     writefln("typeid(PDVA[0]) = %s", typeid(PDVA[0]));
     writefln("typeid(PDVA[1]) = %s", typeid(PDVA[1]));
   }
}

void main()
{
   FOOP fp = &foo;
   auto st = ST!FOOP(fp);
   st.details;
}

The default parameter value types are void, int: a has no default 
and b has an int value as its default.

If I change line 14 from
   FOOP fctn;
to
   POOF fctn;

The default parameter value types are void, void. In other words 
the default value for b is no longer there.

Why doesn't invoking the template (ST!FOOP) replace POOF in line 
14 with FOOP?

Paul

"tcak" <tcak gmail.com> writes:

On Thursday, 25 June 2015 at 04:43:51 UTC, Paul D Anderson wrote:
 I'm trying to pass a function pointer while keeping the default 
 parameter values intact. Given the following:

 [...]

I filed a bug about 2-3 months ago about default parameters 
similar to yours. My guess is that it hasn't been fixed yet, and 
you have hit the same issue.

"Paul D Anderson" <nobody nowhere.none> writes:

On Thursday, 25 June 2015 at 07:10:57 UTC, tcak wrote:
 On Thursday, 25 June 2015 at 04:43:51 UTC, Paul D Anderson 
 wrote:
 I'm trying to pass a function pointer while keeping the 
 default parameter values intact. Given the following:

 [...]

 I filed a bug about 2-3 months ago about default parameters 
 similar to yours. My guess is that it hasn't been fixed yet, 
 and you have hit the same issue.


Thanks

"Paul D Anderson" <nobody nowhere.none> writes:

On Thursday, 25 June 2015 at 14:17:13 UTC, Paul D Anderson wrote:
 On Thursday, 25 June 2015 at 07:10:57 UTC, tcak wrote:
 On Thursday, 25 June 2015 at 04:43:51 UTC, Paul D Anderson 
 wrote:
 I'm trying to pass a function pointer while keeping the 
 default parameter values intact. Given the following:

 [...]

 I filed a bug about 2-3 months ago about default parameters 
 similar to yours. My guess is that it hasn't been fixed yet, 
 and you have hit the same issue.


 Thanks

Turns out this is expected behavior. Default parameter values are 
stripped from function pointers.