On 2/8/23 12:04, John Chapman wrote:
> rather than write it manually for each N?
import std.meta : AliasSeq;
template pickArgs(size_t totalElements,
size_t argsPerElement,
size_t whichElement,
args...) {
alias pickArgs = AliasSeq!();
static foreach (a; 0 .. argsPerElement) {
pickArgs = AliasSeq!(pickArgs, args[whichElement + a *
totalElements]);
}
}
template staticMapN(size_t N, alias fun, args...)
{
static assert(N != 0, "N must be non-zero.");
static assert((args.length % N) == 0,
"Mismatched number of arguments");
enum totalElements = args.length / N;
alias staticMapN = AliasSeq!();
static foreach (e; 0 .. totalElements) {
staticMapN = AliasSeq!(staticMapN,
fun!(pickArgs!(totalElements, N, e, args)));
}
}
// An example struct with some template parameters
struct S(T, size_t length, size_t foo, size_t bar) {
}
// An example template that creates instantiations of the S template
template Instantiate(T, size_t length, size_t foo, size_t bar) {
alias Instantiate = S!(T, length, foo, bar);
}
// Compile-time argument sets for three instantiations of the S template
alias myTypes = AliasSeq!(int, double, long);
alias mySizes = AliasSeq!(1, 2, 3);
alias myFoos = AliasSeq!(42, 43, 44);
alias myBars = AliasSeq!(100, 200, 300);
// A test with those 4 sets of template arguments
alias result = staticMapN!(4, Instantiate, myTypes, mySizes, myFoos,
myBars);
pragma(msg, result);
void main() {
}
I could not figure out eliminating the hard-coded 4. Can we introspect
the parameter list of a template like 'fun' in the example? If we could,
then we could get 4 that way.
Ali
