[Bug 191] New: Cannot refer to member variable in default value for method parameter

[Bruno Medeiros]

Don Clugston wrote:
> Bruno Medeiros wrote:
>> BCS wrote:
>>> Deewiant wrote:
>>>> All I can find about default parameters in the spec is at the 
>>>> "Functions" page,
>>>> where they pop out of the blue in the phrase "A function parameter's 
>>>> default
>>>> value is not inherited", which is all that's said about them. The 
> ....
>>>
>> Hum, quite a catch you got there! Not only should it be better 
>> documented, but maybe it shouldn't work this way.
>> Perhaps the default values should be set not at the call site, but by 
>> the function itself (thus depending on it's run-time type, and not 
>> it's compile-time type),
> 
> I'm almost certain that default values should work that way. They should 
> just be syntactic sugar for overloaded functions.
> Right now, they have the same problem which C++ has -- there's no way 
> that a template can find out what the default values are, and the 
> default values can't be used by function pointers or delegates.
> So for example,
> 
> void foo(int a, int b=2, int c=3) {}
> 
> void goo(int a, int b, int c) { }
> void goo(int a, int b) { goo(a, b, 3); }
> void goo(int a) { goo(a, 2, 3); }
> 
> void function(int) boo;
> 
> foo(7); // ok
> goo(7); // ok
> 
> boo = goo; // ok
> boo(5);
> 
> boo = foo; // doesn't compile -- why not?
> boo(5);
> 
> 

You meant:
   boo = &goo; // ok
   boo(5);

   boo = &foo; // doesn't compile -- why not?


Anyway, "Why not?" ? How could that compile? Even with that syntatic 
sugar the problem would subsist: remember that the expression (&foo) has 
to be evaluable by itself, and if there are many overloads of foo there 
is no way (with that syntax at least) to choose the correct one. (DMD 
currently chooses the lexically first overload)


-- 
Bruno Medeiros - CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D