Re: Template Parameters in Struct Member Functions
On Saturday, 22 August 2015 at 16:49:26 UTC, DarthCthulhu wrote:
I'm having difficulty understanding how templates operate as
function parameters.
Say I have this:
struct ArrayTest {
void arrayTest(T) (T arrayT) {
writeln(arrayT);
}
}
unittest {
ArrayTest test;
float farray[] = [
0.5f, 0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
-0.5f, -0.5f, 0.0f,
-0.5f, 0.5f, 0.0f
];
test.arrayTest(farray);
}
Everything works peachy as expected. But as soon as I add
another parameter to the arrayTest function like so (and
changing the unit test to match):
void arrayTest(T, int passing) (T arrayT) { ... }
I get 'cannot deduce function from argument types' errors.
Specifically stating the type of the function doesn't seem to
help:
test.arrayTest(float [])(farray, 1);
test.arrayTest!(float, 1)(farray);
Re: Template Parameters in Struct Member Functions
On Saturday, 22 August 2015 at 17:08:36 UTC, Mike Parker wrote:
void arrayTest(T, int passing) (T arrayT) { ... }
I get 'cannot deduce function from argument types' errors.
Specifically stating the type of the function doesn't seem to
help:
test.arrayTest(float [])(farray, 1);
test.arrayTest!(float, 1)(farray);
Sorry, that should be:
test.arrayTest!(float[], 1)(farray);
In your template declaration, you have declared two template
parameters, T and passing, and one function parameter, arrayT. It
is equivalent to:
template arrayTest(T, int passing) {
void arrayTest(T arrayT) {...}
}
To call the function, you have to explicitly instantiate the
template with the instantiation operator (which is !) and give it
two arguments as template parameters in the first pair of
parentheses, then you have to give it one function argument in
the second pair of parentheses. The template parameters are
compile-time arguments, the function parameter is runtime.
With this form:
void arrayTest(T)(T arrayT) {...}
There is no need for the explicit instantiation. The compiler is
able to deduce what T should be since it has all the information
it needs, so you can call it like:
test.arrayTest(foo);
