Chepurni multimethods for modern C++

This project implements multimethods with templates for C++17 and higher. For a detailed description, please refer to [Chepurni multimethods for contemporary C++](doc/Chepurni multimethods for contemporary C++.pdf)

multimethod

multimethod template dispatches calls to the first suitable function or a method from the list

Usage:

  multimethod<ReturnType,
    &function1,
    &function2,
    &MyClass::method>::dispatch(a,b);

Requirements to the parameter classes:

• virtual table, e.g. hierarchy defines at least one virtual method
• either enabled RTTI
• or hierarchy defines template instnace_of

matrixdispatch

matrixdispatch template dispatches calls to the best suitable function or a method from the list

Usage:

   matrixdispatch<FunctionType,
    &function1,
    &function2,
    &MyClass::method>::dispatch(a,b);

Requirements to the parameter classes:

• virtual method size_t classID()
• sequentially numbered classes
• backward mapping ID-to-class via DomainA, DomainB classes

FunctionType is a type of the functions, pointed from the matrix.

Performance comparison

Performance is measured with valgrind --tool=callgrind running performance tests perf1 and perf2. Each test dispatches to 40 other functions. (ir) columns contain instructions per call, (s) columns - the wall time per 10000000 loops (for these measurements it matches CPU time) The test executable is build with option NDEBUG=1. std::visit refers to a test, dispatching with std::visit over variant-of-objects, while std::visit* - over variant-of-pointers.

Template	gcc (ir)	clang (ir)	gcc (s)	clang (s)
std::visit	38	35	0.64s	1.0s
std::visit*	58	50	0.93s	1.3s
multimethod	750	702	5.8s	6.4s
matrixdispatch	54	47	0.88s	1.2s

Notes

To compile with Visual Studio use following options /std:c++17 /permissive-