On 07/23/2012 08:25 PM, ReneSac wrote:
How I can return multiple values in D, but one of them being optional? I
tried the 'out' hack to achieve multiple return values, but it didn't
accepted a default argument: it needed a lvalue in the calling function.
Like in C and C++, functions in D can also have a single return value.
The most common workaround in C and C++ has been an out parameter
(pointer in C and pointer or reference in C++).
The options that I can think of:
- Return a struct (or a class) where one of the members is not filled-in
- Similarly, return a tuple
- Use an out parameter, which can have a default lvalue:
int g_default_param;
void foo(ref int i = g_default_param)
{
if (&i == &g_param) {
// The caller is not interested in 'i'
} else {
// The caller wants 'i'
i = 42;
}
}
void main()
{
foo();
int i;
foo(i);
assert(i == 42);
}
- Use some template trick where the caller specifies what he wants:
result = foo();
complex_result = foo!with_iterations_needed();
Thinking back, perhaps because C and C++ don't provide multiple return
values, I never missed them. Although they were nice when coding in
Python. :)
Ali
