On Mon, Nov 03, 2014 at 11:43:42PM +0000, Domingo via Digitalmars-d-learn wrote:
> Hello !
>
> I could not find a clear way that show how to use template types as
> parameter to functions:
>
> There is a general rule to do it ? On several examples when the return type
> comes from a template I saw the usage of "auto" where the compiler will
> deduce the correct type but when we need to pass that value as a parameter
> to a function how we declare then as parameter ?
>
>
> //void dummFunction(type<Bson,Bson,Bson> "appender", type<forFromAuto>
> "another templated type")
>
> void dummFunction(typeforFromAuto "appender", typeforFromAuto "another
> templated type")
> {
> }
Use the typeof operator, for example:
auto myfunc(...) {
struct InternalType { ... }
...
return InternalType(...);
}
void anotherFunc(typeof(myfunc(...)) x) { ... }
void main() {
auto x = myfunc(...);
anotherFunc(x);
}
Using typeof() everywhere is ugly, though, so you could abstract it away
with an alias:
auto myfunc(...) { ... }
alias MyType = typeof(myfunc(...));
void anotherFunc(MyType x) { ... }
...
On the other hand, if anotherFunc() doesn't really need to know what
exact type is passed, you could turn it into a template function:
auto myfunc(...) { ... }
// Now you can pass anything to anotherFunc:
void anotherFunc(T)(T x) { ... }
But passing "anything" may cause problems, if anotherFunc expects x to
have certain methods, but it's not guaranteed to have them:
void anotherFunc(T)(T x) {
...
x.method(); // will fail if T is int, for example
...
}
In this case you can use a signature constraint to limit the scope of
what anotherFunc will accept:
auto myfunc(...) { ... }
void anotherFunc(T)(T x)
if (is(T.init.method())) // test that T has a method called
"method"
{
...
x.method();
...
}
T
--
Being able to learn is a great learning; being able to unlearn is a greater
learning.
