On Wed, Mar 30, 2016 at 06:12:40PM +0000, jmh530 via Digitalmars-d-learn wrote:
> I wrote a version of cartesianProduct that will return the cartesian
> product when the some of the types are not ranges. The original code
> is below.
>
> My issue is that I can't figure out how to turn it into a variadic
> template. The latest thing I tried is:
[...]
Does this do what you want?
import std.algorithm.setops : cartesianProduct;
import std.range : only;
import std.range.primitives;
import std.meta : AliasSeq;
template ImplType(T...)
{
static if (T.length == 0)
alias ImplType = AliasSeq!();
else
{
static if (isInputRange!(T[0]))
alias FirstType = T[0];
else
alias FirstType = typeof(only(T[0].init));
alias ImplType = AliasSeq!(FirstType, ImplType!(T[1 ..
$]));
}
}
auto conditionalOnly(alias fun, T...)(T x) {
ImplType!T y;
foreach (i, e; x) {
static if (isInputRange!(typeof(e)))
y[i] = e;
else
y[i] = only(e);
}
return fun(y);
}
void main() {
import std.stdio;
writeln(conditionalOnly!cartesianProduct(1, [2, 3], 4, [5, 6]));
}
Note that conditionalOnly isn't specifically tied to cartesianProduct;
you can use it on anything that receives a variadic number of range
arguments.
T
--
"I'm not childish; I'm just in touch with the child within!" - RL
