I believe this question was asked before, but here is the
solution again.
struct Foo(_T1, _T2)
{
alias _T1 T1;
alias _T2 T2;
T1 a;
T2 b;
}
FooT.T1 func(FooT, T)(FooT foo, T x)
if (is(FooT.T1) && is(T : FooT.T1))
{
return x * foo.a;
}
void main() {
auto foo = Foo!(size_t, string)(8, "bobcat");
int value = 3;
assert(foo.func(value) == 24);
assert(is(typeof(foo.func(value)) == size_t));
}
- Vijay
On Monday, 12 November 2012 at 12:42:31 UTC, Joseph Rushton
Wakeling wrote:
Suppose that I've got a struct which internally defines a
number of types:
struct Foo(_T1, _T2)
{
alias _T1 T1;
alias _T2 T2;
T1 a;
T2 b;
}
... and now I want to define a function which takes as input an
instance of one of these structs, and a variable of type T1.
I tried the following:
T func(FooT, T = FooT.T1)(FooT foo, T x)
{
return x * foo.a;
}
but found that the type of whatever I was passing would
override the default: e.g. if I called func(fooInstance, 1)
then the second argument would be interpreted as an int even
though Foo.T1 is size_t.
I also tried,
T func(FooT, T : FooT.T1)(FooT foo, T x)
{
return x * foo.a;
}
but this generates a different error: "no property 'T1' for
type 'FooT'". I tried replacing FooT with alias FooT to no
avail.
Obviously I could get round the problems of the first example
with something based around CommonType etc. but I'm just
wondering if it's possible to make an argument dependent on
another template parameter in the way I'm looking for here.
