On Wed, 25 Apr 2012 23:44:07 -0400, Walter Bright
<[email protected]> 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
