Metal is a header-only C++14 library designed to make template metaprogramming intuitive.
#include <metal.hpp>
// First we need some Values
union x { char payload[10]; };
class y { public: char c; };
struct z { char c; int i; };
// ... from which we construct some Lists
using l0 = metal::list<>;
using l1 = metal::prepend<l0, x>;
using l2 = metal::append<l1, z>;
using l3 = metal::insert<l2, metal::number<1>, y>;
static_assert(metal::same<l1, metal::list<x>>::value, "");
static_assert(metal::same<l2, metal::list<x, z>>::value, "");
static_assert(metal::same<l3, metal::list<x, y, z>>::value, "");
// Lists are versatile, we can check their sizes...
static_assert(metal::size<l0>::value == 0, "");
static_assert(metal::size<l1>::value == 1, "");
static_assert(metal::size<l2>::value == 2, "");
static_assert(metal::size<l3>::value == 3, "");
// retrieve their elements...
static_assert(metal::same<metal::front<l3>, x>::value, "");
static_assert(metal::same<metal::back<l3>, z>::value, "");
static_assert(metal::same<metal::at<l3, metal::number<1>>, y>::value, "");
// count those that satisfy a predicate...
static_assert(metal::count_if<l3, metal::trait<std::is_class>>::value == 2, "");
static_assert(metal::count_if<l3, metal::trait<std::is_union>>::value == 1, "");
// We can create new Lists by removing elements...
using l0_ = metal::drop<l3, metal::number<3>>;
using l1_ = metal::take<l3, metal::number<1>>;
using l2_ = metal::erase<l3, metal::number<1>>;
static_assert(metal::same<l0, l0_>::value, "");
static_assert(metal::same<l1, l1_>::value, "");
static_assert(metal::same<l2, l2_>::value, "");
// by reversing the order of elements...
static_assert(metal::same<metal::reverse<l0>, metal::list<>>::value, "");
static_assert(metal::same<metal::reverse<l1>, metal::list<x>>::value, "");
static_assert(metal::same<metal::reverse<l2>, metal::list<z, x>>::value, "");
static_assert(metal::same<metal::reverse<l3>, metal::list<z, y, x>>::value, "");
// by transforming the elements...
using l2ptrs = metal::transform<metal::lazy<std::add_pointer>, l2>;
using l3refs = metal::transform<metal::lazy<std::add_lvalue_reference>, l3>;
static_assert(metal::same<l2ptrs, metal::list<x*, z*>>::value, "");
static_assert(metal::same<l3refs, metal::list<x&, y&, z&>>::value, "");
// even by sorting them...
template<typename x, typename y>
using smaller = metal::number<(sizeof(x) < sizeof(y))>;
using sorted = metal::sort<l3, metal::lambda<smaller>>;
static_assert(metal::same<sorted, metal::list<y, z, x>>::value, "");
// that and much more!
Check out more examples.
Minutes-long compile times are a thing of the past!
You don't have to just take my word for it, see for yourself at metaben.ch.
Don't worry, all your favourite compilers are continuously tested at Travis CI and Appveyor CI.
Compiler | Version | Operating System |
---|---|---|
GCC | 4.8 | Ubuntu 14.04 LTS |
GCC | 4.9 | Ubuntu 14.04 LTS |
GCC | 5 | Ubuntu 14.04 LTS |
GCC | 6 | Ubuntu 14.04 LTS |
GCC | 7 | Ubuntu 14.04 LTS |
Clang | 3.4 | Ubuntu 14.04 LTS |
Clang | 3.5 | Ubuntu 14.04 LTS |
Clang | 3.6 | Ubuntu 14.04 LTS |
Clang | 3.7 | Ubuntu 14.04 LTS |
Clang | 3.8 | Ubuntu 14.04 LTS |
Clang | 3.9 | Ubuntu 14.04 LTS |
Clang | 4.0 | Ubuntu 14.04 LTS |
Clang | 5.0 | Ubuntu 14.04 LTS |
Xcode | 6.4 | OS X 10.10 |
Xcode | 7.3 | OS X 10.11 |
Xcode | 8.0 | OS X 10.11 |
Xcode | 8.1 | OS X 10.12 |
Xcode | 8.2 | OS X 10.12 |
MinGW-w64 | 5 | Windows Server 2012 R2 |
MinGW-w64 | 6 | Windows Server 2012 R2 |
Visual Studio | 14 (2015) | Windows Server 2012 R2 |
Visual Studio | 15 (2017) | Windows Server 2016 |
The complete up to date documentation is available online.
Metal is distributed under the Boost Software License, Version 1.0.