On 29/11/2012 16:27, Dmitry Olshansky wrote:
11/29/2012 7:24 AM, Walter Bright пишет:
The original idea is that there should be *no such thing* as default
construction of a struct as being anything other than T.init. The
default construction of a struct should be a compile time creature, not
a runtime one.
Okay let it be. I'm not against having a defined blank default
constructed object.
Just don't make T() mean it, please!
There are a 0-argument constructor or rather a run-time construction
that need no arguments. Examples are auto-seeded PRNG, empty containers,
digest that typically use default initial vector etc.
Plenty of things. If classes have it why shouldn't structs have one as
well? Is there any reason to introduce this discrepancy?
The sudden change of user-defined run-time construction to a biltblit a
T.init mask once number of arguments is 0 is a nasty surprise and is a
high irregularity in the language.
The unwary may hit a brick wall quite suddenly. Even better example are
constructors with all default args:
//simplified
struct A{
int[] values;
this(int size=10) //default size...
{
values = new int[size];
}
//...
}
A a = A(20); //okay
A b = A(); //try to pick defaults...
assert(b.values is null); // passes - WTF?
Any methods or workarounds to try and make T() produce something
different from T.init is bad D practice. The compiler tries to
statically head them off, but probably should do a better job of that.
Why do we have to use T() syntax for this? It blocks 0-argument
constructor & ones with all defaults.
Default construction is done either way unless avoided with =void and
there is always a T.init. I've spent quite some breath trying to show
how T() is unhelpful in any case one needs a default constructed object.
Totally agree with all this. I can't understand why T() should 'default
construct' T - it's not default anything if you explicitly type T().
static opCall is an ugly workaround especially in generic wrapper code.
Not allowing 0-argument constructors is unintuitive. I have several
times tried reading explanations of why it's like this to no avail. If
you are allowed to call other runtime constructors, why not zero-arg ones?
struct A{...}
A a; // fine, default construct a
A a = A(); // why does this mean the same thing???
I wish we could deprecate the second syntax as we really need to
repurpose it.
