On 29/11/2012 12:10, Maxim Fomin wrote:
On Thursday, 29 November 2012 at 10:41:46 UTC, Mehrdad wrote:
I'm just not understanding the whole "the default construction of a
struct should be a compile time creature, not a runtime one".
Don't you have to initialize the struct with zero's either way?
So either way, you're going to have to initialize it... so no perf
increase in any way. Why prevent the user from default-initializing it
the way he wants to?
Every type has a CT-known default initializer, even classes have (null).
If structures had a runtime one, this would break code (especially
templates and CTFE) which relies on knowing something about constant
default instance of a type at CT.
extern bool foo();
struct S
{
int i;
this() {
i = foo() ? 1 : -1;
}
}
---------
S s;
dosmth(s);
---------
//somewhere in Phobos
void dosmth(T) (T obj)
{
T val; // is i 0, -1 or 1 ?
}
I think s.i and val.i should be zero. S.this() should never be called
implicitly IMO, but instead like this:
// runtime code
S s = S();
These two should always be equivalent, and compile-time evaluated:
S s;
S s = S.init;
If we actually need non-trivial compile-time 'default' constructors,
they should have a different syntax:
// runtime ctors
this();
this(int x = 0);
this(T...)(T args);
// CT ctor (if actually needed)
default this(){...}
S.init would imply a call to the above CT constructor.
