Metal - Metaprogramming Algorithms

Metal is a header-only C++14 library designed to make metaprogramming easy.

Modern

// 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...
template<typename T>
using is_class = metal::as_number<std::is_class<T>>;

template<typename T>
using is_union = metal::as_number<std::is_union<T>>;

static_assert(metal::count_if<l3, metal::lambda<is_class>>::value == 2, "");
static_assert(metal::count_if<l3, metal::lambda<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::lambda<std::add_pointer_t>, l2>;
using l3refs = metal::transform<metal::lambda<std::add_lvalue_reference_t>, 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.

Blazing Fast

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.

Portalble

Don't worry, all your favourite compilers are continuously tested at Travis CI and Appveyor CI.

Compiler	Version	Operating System
GCC	5	Ubuntu 14.04 LTS
GCC	6	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
Visual Studio	14 (2015)	Windows Server 2012 R2
MinGW-w64	5	Windows Server 2012 R2

Documentation

The complete up to date documentation is available online.

Alternatively, an offline copy may be obtained by either cloning branch gh-pages

git clone https://github.com/brunocodutra/metal.git --branch=gh-pages doc/html

or locally building target doc (CMake and Doxygen required)

cmake /path/to/Metal
cmake --build . --target doc

Either way, just open doc/html/index.html on your favourite web browser.

License