www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.bugs - [Issue 14736] New: Function Default Parameters Are Lost


          Issue ID: 14736
           Summary: Function Default Parameters Are Lost
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Windows
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: paul.d.anderson comcast.net

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);

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;
  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?

I don't know if this is related to #3646. If it is, the status of FIXED may be

Jun 25 2015