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fu2::function an improved drop-in replacement to std::function

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Provides improved implementations of std::function:

that provide many benefits and improvements over std::function:

Table of Contents

Documentation

How to use

function2 is implemented in one header (function.hpp), no compilation is required. Just copy the function.hpp header in your project and include it to start. It's recommended to import the library as git submodule using CMake:

# Shell:
git submodule add https://github.com/Naios/function2.git

# CMake file:
add_subdirectory(function2)
# function2 provides an interface target which makes it's
# headers available to all projects using function2
target_link_libraries(my_project function2)

Use fu2::function as a wrapper for copyable function wrappers and fu2::unique_function for move only types. The standard implementation std::function and fu2::function are convertible to each other, see the chapter convertibility of functions for details.

A function wrapper is declared as following:

fu2::function<void(int, float) const>
// Return type ~^   ^     ^     ^
// Parameters  ~~~~~|~~~~~|     ^
// Qualifier ~~~~~~~~~~~~~~~~~~~|

Constructing a function

fu2::function and fu2::unique_function (non copyable) are easy to use:

fu2::function<void() const> fun = [] {
  // ...
};

// fun provides void operator()() const now
fun();

Non copyable unique functions

fu2::unique_function also works with non copyable functors/ lambdas.

fu2::unique_function<bool() const> fun = [ptr = std::make_unique<bool>(true)] {
  return *ptr;
};

// unique functions are move only
fu2::unique_function<bool() const> otherfun = std::move(fun):

otherfun();

Non owning functions

A fu2::function_view can be used to create a non owning view on a persistent object. Note that the view is only valid as long as the object lives.

auto callable = [ptr = std::make_unique<bool>(true)] {
  return *ptr;
};

fu2::function_view<bool() const> view(callable);

Convertibility of functions

fu2::function, fu2::unique_function and std::function are convertible to each other when:

Convertibility from \ tofu2::functionfu2::unique_functionstd::function
fu2::functionYesYesYes
fu2::unique_functionNoYesNo
std::functionYesYesYes
fu2::function<void()> fun = []{};
// OK
std::function<void()> std_fun = fun;
// OK
fu2::unique_function<void()> un_fun = fun;

// Error (non copyable -> copyable)
fun = un_fun;
// Error (non copyable -> copyable)
fun = un_fun;

Adapt function2

function2 is adaptable through fu2::function_base which allows you to set:

struct my_capacity {
  static constexpr std::size_t capacity = sizeof(my_type);
  static constexpr std::size_t alignment = alignof(my_type);
};

The following code defines an owning function with a variadic signature which is copyable and sfo optimization is disabled:

template<typename Signature>
using my_function = fu2::function_base<true, true, fu2::capacity_none, true, false, Signature>;

The following code defines a non copyable function which just takes 1 argument, and has a huge capacity for internal sfo optimization. Also it must be called as r-value.

template<typename Arg>
using my_consumer = fu2::function_base<true, false, fu2::capacity_fixed<100U>,
                                       true, false, void(Arg)&&>;

// Example
my_consumer<int, float> consumer = [](int, float) { }
std::move(consumer)(44, 1.7363f);

Performance and optimization

Small functor optimization

function2 uses small functor optimization like the most common std::function implementations which means it allocates a small internal capacity to evade heap allocation for small functors.

Smart heap allocation moves the inplace allocated functor automatically to the heap to speed up moving between objects.

It's possible to disable small functor optimization through setting the internal capacity to 0.

Coverage and runtime checks

Function2 is checked with unit tests and valgrind (for memory leaks), where the unit tests provide coverage for all possible template parameter assignments.

Compatibility

Tested with:

Every compiler with modern C++14 support should work. function2 only depends on the standard library.

License

function2 is licensed under the very permissive Boost 1.0 License.

Similar implementations

There are similar implementations of a function wrapper:

Also check out the amazing CxxFunctionBenchmark which compares several implementations.