out default argument of void

[Ali Çehreli]

On 01/04/2012 02:19 PM, Caligo wrote:
 > I have a function that looks something like this:
 >
 > bool fun(double theta, out A a, out B b, out C c){  /* ... */ }
 >
 > if fun() returns false, then nothing is supposed to be assigned to a,
 > b, c.  If it returns true, then values are assigned to a, b, c.  Also,
 > there are two ways to call fun():  If I'm interested in the return
 > value only, then
 >
 > 1. fun(theta);
 >
 > otherwise,
 >
 > 2. fun(theta, a, b, c);

How about providing the results always as return values:

import std.exception;

alias int A;
alias int B;
alias int C;

bool fun(double)
{
     return true;
}

struct ABC
{
     A a;
     B b;
     C c;
}

struct FunResult
{
     ABC * abc;

     @property bool isValid() const
     {
         return abc !is null;
     }

     @property A a() const
     {
         enforce(abc);
         return abc.a;
     }

     // etc.
}

FunResult funWithResult(double)
{
     return FunResult(new ABC);
}

void main()
{
     auto isValid = fun(1.1);

     auto result = funWithResult(2.2);
     if (result.isValid) {
         auto use = result.a;
     }
}

Ali