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D - Does D support default arguments?

reply "Andrew Edwards" <edwardsac spamfreeusa.com> writes:
If so, how does one use this feature?

Thanks in advance,
Andrew
Jul 04 2003
parent reply "Carlos Santander B." <carlos8294 msn.com> writes:
"Andrew Edwards" <edwardsac spamfreeusa.com> escribiσ en el mensaje
news:be5863$ibk$1 digitaldaemon.com...
|

No, it doesn't. You should use function overloading. Instead of:

int foo(int a,int b=0) {...}

You should write:

int foo(int a) { foo(a,0); }
int foo(int a,int b) { ....}

—————————————————————————
Carlos Santander


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Jul 04 2003
parent reply "Andrew Edwards" <edwardsac spamfreeusa.com> writes:
"Carlos Santander B." <carlos8294 msn.com> wrote in message
news:be5a2l$jrq$1 digitaldaemon.com...

 "Andrew Edwards" <edwardsac spamfreeusa.com> escribiσ en el mensaje
 news:be5863$ibk$1 digitaldaemon.com...
 |

 You should write:

 int foo(int a) { foo(a,0); }
 int foo(int a,int b) { ....}


how does this apply to the following situation?

class someClass
{
    this()
    {
      void func(){}
    }

    this(inout uint t)
    {
      void func(inout uint t){}
    }

    this(inout uint t, inout z)
    {
      void func(inout uint t, inout uint z){}
    }

    // suggested fix
    this(inout uint t)
    {
      func(t, 0);
    }
}

I would like to provide a default argument for z; however, since I've
already overloaded this(inout uint t) to do something else, overloading it
again as suggested would result in ambiguity. Wouldn't it?
Jul 04 2003
next sibling parent "Andrew Edwards" <edwardsac spamfreeusa.com> writes:
Sorry...


     // suggested fix
     this(inout uint t)
     {
       func(t, 0);
     }


should read:


     // suggested fix
     this(inout uint t)
     {
       this(t, 0);
     }
Jul 04 2003
prev sibling next sibling parent reply "Carlos Santander B." <carlos8294 msn.com> writes:
"Andrew Edwards" <edwardsac spamfreeusa.com> escribiσ en el mensaje
news:be5cnt$m25$1 digitaldaemon.com...
| how does this apply to the following situation?
|
| class someClass
| {
|     this()
|     {
|       void func(){}
|     }
|
|     this(inout uint t)
|     {
|       void func(inout uint t){}
|     }
|
|     this(inout uint t, inout z)
|     {
|       void func(inout uint t, inout uint z){}
|     }
|
|     // suggested fix
|     this(inout uint t)
|     {
|       func(t, 0);
|     }
| }
|

That's really odd (for me, at least), because you need an inout parameter,
so there's no logical reason for having it as default, because it must be a
reference. About having two identical functions, well, they should do the
same thing, shouldn't they? I mean, they're both constructors, so they
should be behaving *at least* in similar ways.

—————————————————————————
Carlos Santander


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Jul 04 2003
parent "Andrew Edwards" <edwardsac spamfreeusa.com> writes:
"Carlos Santander B." <carlos8294 msn.com> wrote...


 That's really odd (for me, at least), because you need an inout parameter,
 so there's no logical reason for having it as default, because it must be


a

 reference. About having two identical functions, well, they should do the
 same thing, shouldn't they? I mean, they're both constructors, so they
 should be behaving *at least* in similar ways.


For the inexperienced, nothing seems "odd" the first time around! I guess
have a lot of learning left to do. Given time, and people like yourself who
take time to answer my brain-dead question, I will get the hang of this!

The previous example was my closest "guestimation" of what was happening in
a C++ program. Learning has occurred!

Thanks,
Andrew
Jul 05 2003
prev sibling parent Ilya Minkov <midiclub 8ung.at> writes:
Andrew Edwards wrote:


 I would like to provide a default argument for z; however, since I've
 already overloaded this(inout uint t) to do something else, overloading it
 again as suggested would result in ambiguity. Wouldn't it?


Default arguments are also a kind of overloading in C++. You can imagine 
that like simple functions which are generated in-line.

Taken the call

	func(t, 0);

how should it be supposed to know, which function to choose??? Both are 
perfectly good substitutes.

consider another stupid situation:

	func(t, 0, 3);

It knows that it is to choose the function with 3 parameters. However, 
the parameter where 3 is passed is inout, which means a function can 
write into it. 3 is a constant. How do you write into a constant? And 
this is the kind of expansion which is done for default parameters.

What you probably want is a global variable, which you shall pass into 
the function, or use the first overloaded one, or DISAMBIGUATE NAMES.

Mind: overusing overloading will bite you, since in case you are 
assigning different behaviour to overloads, you need to think at any 
function call what function exactly is called, and why exactly some 
other overload is not. Even if you manage to get it right, adding 
another overloaded form will most certainly break your code.

-i.
Jul 05 2003