construct — Boost.HigherOrderFunctions 0.6 documentation

# construct

## Header

    #include <boost/hof/construct.hpp>

## Description

The `construct` function returns a function object that will construct the object when the called. A template can also be given, which it will deduce the parameters to the template. The `construct_meta` can be used to construct the object from a metafunction.

## Synopsis

    // Construct by decaying each value
    template<class T>
    constexpr auto construct();

    template<template<class...> class Template>
    constexpr auto construct();

    // Construct by deducing lvalues by reference and rvalue reference by reference
    template<class T>
    constexpr auto construct_forward();

    template<template<class...> class Template>
    constexpr auto construct_forward();

    // Construct by deducing lvalues by reference and rvalues by value.
    template<class T>
    constexpr auto construct_basic();

    template<template<class...> class Template>
    constexpr auto construct_basic();

    // Construct by deducing the object from a metafunction
    template<class MetafunctionClass>
    constexpr auto construct_meta();

    template<template<class...> class MetafunctionTemplate>
    constexpr auto construct_meta();

## Semantics

    assert(construct<T>()(xs...) == T(xs...));
    assert(construct<Template>()(xs...) == Template<decltype(xs)...>(xs...));
    assert(construct_meta<MetafunctionClass>()(xs...) == MetafunctionClass::apply<decltype(xs)...>(xs...));
    assert(construct_meta<MetafunctionTemplate>()(xs...) == MetafunctionTemplate<decltype(xs)...>::type(xs...));

## Requirements

MetafunctionClass must be a:

- MetafunctionClass

MetafunctionTemplate<Ts...> must be a:

- Metafunction

T, Template<Ts..>, MetafunctionClass::apply<Ts...>, and MetafunctionTemplate<Ts...>::type must be:

- MoveConstructible

## Example

    #include <boost/hof.hpp>
    #include <cassert>
    #include <vector>

    int main() {
        auto v = boost::hof::construct<std::vector<int>>()(5, 5);
        assert(v.size() == 5);
    }