Dispatch

poet::dispatch maps runtime integers to compile-time specializations.

Single parameter

struct Kernel {
    template<int N>
    int operator()(int x) const {
        return N + x;
    }
};

int result = poet::dispatch(
    Kernel{},
    poet::dispatch_param<poet::inclusive_range<0, 4>>{choice},
    10);

poet::inclusive_range<Start, End> is inclusive on both ends.

Multiple parameters

Pass multiple dispatch_param objects to dispatch over a cartesian product:

auto result = poet::dispatch(
    Kernel2D{},
    poet::dispatch_param<poet::inclusive_range<1, 4>>{rows},
    poet::dispatch_param<poet::inclusive_range<1, 4>>{cols},
    data);

The tuple form is equivalent:

auto params = std::make_tuple(
    poet::dispatch_param<poet::inclusive_range<1, 4>>{rows},
    poet::dispatch_param<poet::inclusive_range<1, 4>>{cols});

poet::dispatch(Kernel2D{}, params, data);

Sparse combinations

Use dispatch_set when only specific tuples are valid:

using Shapes = poet::dispatch_set<int,
    poet::tuple_<2, 2>,
    poet::tuple_<4, 4>,
    poet::tuple_<2, 4>>;

poet::dispatch(MatMul{}, Shapes{rows, cols}, a, b, c);

Error handling

The default behavior on a miss is:

void return: do nothing
non-void return: return R{}

Use poet::throw_on_no_match when a miss should fail:

auto result = poet::dispatch(
    poet::throw_on_no_match,
    Kernel{},
    poet::dispatch_param<poet::inclusive_range<0, 4>>{choice},
    10);

The same tag works with dispatch_set.

Runnable examples

examples/dispatch.cpp — single and multi-parameter dispatch. Try on Compiler Explorer
examples/dispatch_set.cpp — sparse combinations and throw_on_no_match. Try on Compiler Explorer
examples/polynomial.cpp — Horner’s method specialised on a runtime-chosen degree, combined with static_for to unroll the recurrence. Try on Compiler Explorer

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