On Sat, 10 Dec 2011 02:42:30 -0500, Andrew Wiley
<wiley.andre...@gmail.com> wrote:
On Sat, Dec 10, 2011 at 1:23 AM, Andrew Wiley <wiley.andre...@gmail.com>
wrote:
Is there a syntax that allows me to specify arguments to a templated
constructor for a struct? The intuitive way looks like this, but it
doesn't work.
---
struct Test {
this(T, bool b)(T info) if((b && something ) || (!b &&
somethingElse)) {
}
}
void main() {
Test test = Test!(int, true)(5); // Error: template instance
Test!(int,true) Test is not a template declaration, it is a struct
}
---
Looks like I can work around it by doing this:
---
template makeTest(T, bool b) {
static if((b && something) || (!b && somethingElse)) {
alias Test makeTest;
}
else static assert(0, "some error message");
}
struct Test {
private:
this(T)(T info) {
}
}
void main() {
Test test = Test!(int, true)(5); // Error: template instance
Test!(int,true) Test is not a template declaration, it is a struct
}
---
But this solution isn't very satisfying because Test is no longer
directly protected by the static checks I want.
A constructor is just a function. Use an IFTI-able function instead:
Test makeTest(bool b, T)(T info) {...; return Test(realCtorArgsHere);}
As a bonus, you don't have to specify T because of IFTI (which is why I
made it the second template parameter).
C++ and D are full of little trinkets like this. The earliest example I
can remember is std::make_pair from C++.
-Steve
