On Sunday, 12 March 2017 at 18:49:22 UTC, data pulverizer wrote:
Hello all,
I am attempting to write templates for differently qualified
types using specialisations. Below is an example for const and
non-const outlining my approach:
``````````````````````````
import std.stdio : writeln;
import std.traits : ConstOf;
auto max(T)(T x, T y)
{
writeln("General template");
return x > y ? x : y;
}
auto max(T: ConstOf!U, U)(T* x, T* y)
{
writeln("Const template");
return *x > *y ? x : y;
}
void main(){
const double p = 2.4, q = 3;
writeln(max(&p, &q));
}
``````````````````````````
I get this output:
General template
7FFE5B3759A8
In this case would like to use the ConstOf specialisation
instead of the default implementation for the inputs which are
const.
Thanks for you answers in advance
You need to make one little change for this to work:
import std.stdio : writeln;
import std.traits : ConstOf;
auto max(T)(T x, T y)
{
writeln("General template");
return x > y ? x : y;
}
auto max(T: const U, U)(T* x, T* y) <----- Changed `ConstOf!U` to
`const U`
{
writeln("Const template");
return *x > *y ? x : y;
}
void main(){
const double p = 2.4, q = 3;
writeln(max(&p, &q)); //Prints "Const template"
}
The reason this doesn't work is when you use ConstOf!U, it's not
looking for a `const U`, it's looking for the type `ConstOf!U`.
I'm not sure if this is a bug or not... Anyway, this will also
work if we change the following:
void main(){
ConstOf!double p = 2.4, q = 3; <----- Changed `const double` to
`ConstOf!double`
writeln(max(&p, &q)); //Prints "Const template"
}
