What to do about default function arguments

[Steven Schveighoffer]

On Wed, 25 Apr 2012 23:44:07 -0400, Walter Bright  
<newshound2 at digitalmars.com> wrote:

> A subtle but nasty problem - are default arguments part of the type, or  
> part of the declaration?
>
>     See http://d.puremagic.com/issues/show_bug.cgi?id=3866
>
> Currently, they are both, which leads to the nasty behavior in the bug  
> report.
>
> The problem centers around name mangling. If two types mangle the same,  
> then they are the same type. But default arguments are not part of the  
> mangled string. Hence the schizophrenic behavior.
>
> But if we make default arguments solely a part of the function  
> declaration, then function pointers (and delegates) cannot have default  
> arguments. (And maybe this isn't a bad thing?)

Some testing (2.059):

void main()
{
     auto a = (int x = 1) { return x;};
     auto b = (int x) { return x;};
     pragma(msg, typeof(a).stringof);
     pragma(msg, typeof(b).stringof);
}

output:

int function(int x = 1) pure nothrow @safe
int function(int x = 1) pure nothrow @safe

second pass:

void main()
{
     auto a = (int x = 1) { return x;};
     pure nothrow @safe int function(int) b = (int x) { return x;};
     pragma(msg, typeof(a).stringof);
     pragma(msg, typeof(b).stringof);
     b = a; // ok
     //a = b; // error

     //b(); // error
}

output:

int function(int x = 1) pure nothrow @safe
int function(int)


if you ask me, everything looks exactly as I'd expect, except the auto  
type inference of b.  Can this not be fixed?  I don't understand the  
difficulty.

BTW, I didn't know you could have default arguments for  
functions/delegates, it's pretty neat :)

-Steve