On Wednesday, 18 September 2013 at 05:28:41 UTC, Timothee Cour
wrote:
This may have been discussed before, but I'm not sure whether
this is a bug
or not. In any case it's a bit confusing.
struct Foo2{
this(T...)(T args){
assert(0);
}
}
void main(){
auto a2=Foo2();//doesn't call assert(0) (ie this(T...) not
called)
}
There is no "argument-less constructor" in D. "Struct()" is just
shorthand for "Struct.init" (bar a few exceptional exceptions:
@disabled this() and static opCall).
AFAIK, D decided to not have "default" constructors, as it goes
against a few other features (compile time known init state,
compile time statics). However, not having a constructor which
has "0 arguments" is a gratuitous historical limitation.
Chances are it won't change any time soon (or ever).
Workarounds include:
//----
//
Calling "__ctor" explicitly:
Foo2 foo2;
foo2.__ctor();
(IMO god awful solution)
//----
//
Using static opCall instead of constructor:
struct Foo2
{
Foo2 static opCall(T...)(T args)
{
Foo2 ret;
//Do something.
return ret;
}
}
Foo2 foo2 = Foo2(); //Calls opCall
A bit hackish, but works. Unfortunately, this is not a
"construction" sequence, so you won't be able to use it with
emplace, for example.
//----
//
A non-member free function. Similar to static opCall, but a bit
less hackish. Just create a free function (usually named the same
as your struct, but lowercased).
This is also used a lot in Phobos, as it can prevent direct use
of the struct:
private struct Foo2Result
{
}
public auto foo2(T...)(T args)
{
Foo2 ret;
//Do something.
return ret;
}
auto myFoo2 = foo2(); //Calls the function.
