mlib is a fast, simple c++ metaprogramming library that uses c++20. That also has a tiny bit of reflection!
#include<tuple> // std::tuple
#include<iostream> // std::cout
#include<utility> // std::make_index_sequence
#include "for_each.hpp" // mlib::for_each
#include "tuple.hpp" // mlib::tuple
#include "transform.hpp" // mlib::transform
#include "select.hpp" // mlib::select
#include "find.hpp" // mlib::find
#include "tuple_reverse.hpp" // mlib::tuple_reverse
#include "constexpr_for.hpp" // mlib::constexpr_for
#include "constexpr_while.hpp" // mlib::constexpr_while
#include "refl_get.hpp" // mlib::refl_get
#include "get_nth_element.hpp" // mlib::get_nth_element
#include "pack.hpp" // mlib::value_pack
#include "constexpr_map.hpp" // mlib::constexpr_map
#include "count_if.hpp" // mlib::count_if
#include "pack_find.hpp" // mlib::pack_find
#include "parse_rules.hpp" // mlib::parse_rules
#include "constexpr_switch.hpp"// mlib::constexpr_switch
#include "constexpr_range.hpp" // mlib::constexpr_range
int main()
{
// mlib::for_each
std::tuple<int, char, bool, double> t{ 42, 'c', true, 3.142 };
mlib::for_each(t, [](auto& t) { std::cout << "val: " << t << "\n"; });
// mlib::transform
std::tuple<int, char, double> t2{ 42, 'c', 3.142 };
mlib::transform(t2, [](auto& t) {return static_cast<int>(t); });
// mlib::select
std::tuple<char, bool, double> t3{ 'c', true, 3.142 };
auto tuple = mlib::select(t3, std::index_sequence<1, 2>{});
mlib::for_each(tuple, [](auto& t) {std::cout << "val: " << t << "\n"; });
// note need to add to less than: --\/, will print one hello.
mlib::constexpr_while < 0, [](int t) {t++; return t < 3; }, [&]() {std::cout << "Hello\n"; }, [](int t) {return t + 1; } > ();
// highest number of recursion.
mlib::constexpr_while < 0, [](int t) {t++; return t < 501; }, [&]() {std::cout << "."; }, [](int t) {return t + 1; } > ();
struct foo { int a; double b; char c; };
foo f{42, 3.14, 'c'};
auto x = mlib::meta::refl_get<foo>(f);
std::cout << std::get<0>(x);
std::cout << mlib::get_nth_element<2>(42, 'c', 3.14, true) << "\n"; // returns 3.14
mlib::value_pack<42, 'c', 3.142, true> v{};
mlib::constexpr_map < mlib::member_map<42, 'c'>{}, mlib::member_map<true, 3.142>{} > map{};
std::cout << map[mlib::constexpr_parameter<true>{}];
constexpr auto z = map.lookup<42>();
std::cout << z;
std::tuple tuple_count{ 0, 31.4, 5, 7, 0 };
std::cout << mlib::count_if([](auto t) {return t > 0; }, tuple_count);
std::cout << mlib::pack_find<42, 'c', true, 3, 12, 'b', 42, false, 5, 'y'>();
std::cout << mlib::pack_find<'n', 'c', true, 3, 12, 'b', 42, false, 5, 'y'>();
constexpr auto fixed = mlib::fixed_string{ "hello this is me" };
constexpr auto result_of_branches =
mlib::parse_rules<fixed>{}.if_has_character<'c'>([&](auto x) {return mlib::fixed_string{ "ey i don't want a aije" }; })
.if_has_character<'a'>([&](auto x) {return mlib::fixed_string{ "I dont wnt n eiy" }; })
.if_has_character<'t'>([&](auto x) {return mlib::fixed_string{ "I dont think that this will happen\n" }; })
.if_has_character<' '>([&](auto x) {return mlib::fixed_string{ x.data }; });
mlib::constexpr_switch <
5, [](mlib::constexpr_parameter<0>) { std::cout << "it is 0\n"; },
[](mlib::constexpr_parameter<5>) { std::cout << "it is not 0\n"; },
[](auto) { std::cout << "I don't know what it is!\n"; } >
value{};
value();
constexpr auto value_index = mlib::constexpr_range<1, 2, 3, 4, 5, 6>{}
.add<5>()
.pop_front()
.map < [](auto x) {return x + 1; } > ()
.map_with_location < [](auto x, auto idx) {return x + idx; } > ()
.join_with<0, 1, 2, 3, 4>()
.add(mlib::Size{})
.remove<0>()
.at<10>();
}mlib::for_each is a constexpr function that takes two arguements std::tuple and a callable, for instance a lambda. mlib::for_each's has the following outline:
template<typename T, typename... Ts>
constexpr auto for_each(std::tuple<T, Ts...>& tup, auto& callable)
{
// delegate to for_each_impl
}An example use case is passing a lambda expression that outputs the elements in the std::tuple:
std::tuple<int, char, bool, double> t{42, 'c', true, 3.142};
mlib::for_each(t, [&](auto& a){std::cout << t << ", ";})And the output would be the following:
42, c, t, 1, 3.142,
The benchmark for this is as follows:
------------------------------------------------------
Benchmark Time CPU Iterations
------------------------------------------------------
BM_for_each 144 ns 82.6 ns 8173558
mlib::transform is a constexpr function takes a given tuple, t and a given function f that transforms one of the elements inside of the tuple. An example invocation of mlib::transfrom looks like this:
std::tuple t{1, 4, 7, 'c', true, false};
mlib::transform(t, [](auto& t){return decltype(t)(static_cast<int>(t));});This invokation, has a tuple t: std::tuple<int, char, bool> and then transforms that tuple using the [](auto t) { return (static_cast<int>(t)) + 1; };, and does so accordingly.
mlib::transform's implementation looks like this:
template <typename... Ts, std::size_t... indexes>
constexpr auto transform_helper(std::tuple<Ts...> t, auto lambda,
std::index_sequence<indexes...> i_s) {
return std::make_tuple(lambda(std::get<indexes>(t))...);
}
template <typename T, typename... Ts>
constexpr auto transform(std::tuple<T, Ts...> t, auto lambda) {
return transform_helper(t, lambda,
std::make_index_sequence<sizeof...(Ts)>{});
}It is a very simple implementation, and mlib::transform is a great tool.
The benchmark is as follows:
-------------------------------------------------------
Benchmark Time CPU Iterations
-------------------------------------------------------
BM_Transform 307 ns 173 ns 3620400
mlib::transform is a string that can be used at compile time, so the size needs to be known at compile time and needs to be passed as an NTTP or it can be infered by the constexpr constructor. Here is how you would have a compile time string, using fixed_string:
fixed_string<6> f{"hello"}; // note that `fixed_string` has a `constexpr` constructor taking an array.The only hardship is specifying the NTTP. An example implementation of fixed_string is like this:
template<auto I> // I is the size of the string
struct fixed_string
{
// notice the constexpr constructor.
constexpr fixed_string(char(&arr)[I])
{
// copies `arr` into `m_data`
}
char m_data[I] = {};
};mlib::all_of is a simple feature that checks if all of the booleans, bools passed in are all true. A simple example is as follows:
mlib::all_of(true, true, 6 == 6, true, 42 == 0, true); // falseAnother example is as follows:
mlib::all_of(true, true, true, true); // trueSo it is a very useful feature, and can be used in many different ways, and example implementation of mlib::all_of is as follows:
namespace mlib
{
template<bool b, bool... bs>
struct all_of
{
static constexpr auto value = b && all_of<bs...>::value;
};
template<bool b>
struct all_of<b>
{
static constexpr auto value = b;
};
} // namespace mlibmlib::amount allows you do do things like you would do in a run time loop but at compile time. You can specify the number of recursions in the <> template parameter part. It is a very easy think to use, and can happen at compile time, as long as the callable passed in can run at compile time. Here is an example usage:
amount<10>.times([](){std::cout << "hello" << "\n";}); // note that this doesn't happen at compile time
amount<10>.times([](){0 + 257;}); // happens at compile time, but the result isn't really observable.So, as shown it is a very useful feature. An example implementation is as follows:
template<auto T>
struct amount
{
constexpr auto times(auto&& lambda) const;
};
template<auto T>
static constexpr auto amount_t = amount<T>{};
template<auto T>
constexpr auto amount<T>::times(auto&& lambda) const
{
lambda();
if constexpr (T - 1 != 0)
{
amount_t<T - 1>.times(lambda);
}
return true;
}mlib::one_of is a compile time or. You pass in a bunch of bools, and if one of then is true, the value that the class mlib::one_of holds will be true. An example use of mlib::one_of is as follows:
bool b = mlib::one_of<false, false, false>::value; // b == false
bool c = mlib::one_of<false, false, true, false, false>::value; // c == trueSo it is very easy to use. An example implementation of mlib::one_of is as follows:
namespace mlib
{
template<bool b, bool... b>
struct one_of
{
static constexpr bool value = (b || b...);
};
template<bool b>
struct one_of
{
static constexpr bool value = b;
};
} // namespace mlibAnd thats it for its implementation, note that it's implementation is not recursive!
mlib::constexpr_map is a compile-time map that also allows compile time lookup using the operator[] which takes a mlib::constexpr_parameter as it's compile time arguement and a constexpr lookup function lookup which takes the value to be looked up as a non type template parameter. It has a very cool implementation here is a watered down version of what it looks like:
template<auto T> struct constexpr_parameter {using type = decltype(T);}
template<auto A, auto B> struct member_map {
constexpr auto operator[](constexpr_parameter<A>)
{
return B;
}
};
template<auto... members> struct constexpr_map : constexpr_parameter<members>::type...
{
using decltype(members)::operator[]...;
// note lookup is missed out here
};But as you can see it is a very cool implementation. Now onto some examples using mlib::constexpr_map:
mlib::constexpr_map<mlib::member_map<'c', 4>{}, mlib::member_map<true, 42>{}> map{};
std::cout << map[mlib::c_p<'c'>];Note that here we are using mlib::c_p which is just a mlib::constexpr_parameter it looks like this:
template<auto T>
constexpr auto c_p = constant_parameter<T>{};So in conclusion, mlib::constexpr_map is a really cool feature, the only problem is that the map is constexpr so therefore cannot add values, change values, etc.
mlib::meta::relf_get is a useful reflection, that gets all of the members out of a struct for example if you had a struct a:
struct a
{
int a;
char c;
bool b;
};and so if pass an instance of a like this: a A{42, 'c', true}; to refl_get we will get a tuple with the contents of std::tuple<int, char, bool>{42, 'c', true}! It is as easy as that to reflect this!
It looks like this:
constexpr auto refl_get(auto& t)
{
// implementation
}mlib::string_parse is a struct taking an mlib::fixed_string, str as a NTTP. It then has member functions:
- mlib::string_parse::substr
- mlib::string_parse::consume_until
This, mlib::string_parse is a very basic example of compile-time string parsing. An example of how mlib::string_parse looks like is as follows:
template<mlib::fixed_string str>
struct string_parse
{
template<auto Start, auto End>
constexpr auto substr() -> mlib::fixed_string<End - Start>;
template<char C>
constexpr auto consume_until() -> mlib::fixed_string;
template<char C>
constexpr auto blur_with() const noexcept;
template<char c, int X>
constexpr auto blur_until() const noexcept;
};
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