• via Digitalmars-d-bugs (54/54) Jun 25 2015 https://issues.dlang.org/show_bug.cgi?id=14736

via Digitalmars-d-bugs <digitalmars-d-bugs puremagic.com> writes:

https://issues.dlang.org/show_bug.cgi?id=14736

          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);
  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?


wrong.

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