使用boost :: optional时避免临时 [英] Avoiding temporary when using boost::optional

问题描述

boost ::可选支持in_place构造，如下所示:

boost::optional support in_place construction like so:

#include <boost/optional.hpp>
#include <boost/utility/typed_in_place_factory.hpp>

class Foo
{
    int a,b;

  public:
    Foo(int one, int two) : a(one),b(two) {}
};


int main()
{
    boost::optional<Foo> fooOpt(boost::in_place<Foo>(1,3));
}

一旦有了初始化的fooOpt，是否可以在不创建临时Foo的情况下为其分配新的Foo?

Once we have an initialized fooOpt, is there a way of assigning a new Foo to it without creating a temporary?

类似的东西:

fooOpt = boost::in_place<Foo>(1,3);

谢谢！

推荐答案

boost :: optional

#include <boost/optional.hpp>

int main() {
    boost::optional<int> x;
    x = boost::in_place(3);
}

我们还可以通过使Foo从boost::noncopyable继承来显示(通过代码)这是就地构建对象:

We can also show (via code) that this is building the object in-place by making Foo inherit from boost::noncopyable:

#include <boost/optional.hpp>
#include <boost/noncopyable.hpp>

class Foo : boost::noncopyable {
    public:
        Foo(int one, int two) {}
};


int main() {
    boost::optional<Foo> x;
    x = boost::in_place(3, 4);
}

std :: optional(最终...)

最终，我们将可以访问std::optional.此类型将实现emplace()方法，该方法还将实现就地构造.

std::optional (eventually...)

Eventually, we will get access to std::optional. This type will implement an emplace() method, that will implement in-place construction as well.

#include <optional>

int main() {
    std::optional<int> x;
    x.emplace(3);
}

boost :: optional(很快...)

在版本1.56.0中，boost::optional还将实现我在std :: optional中讨论的emplace()方法.因此，让我们来看一下:

boost::optional (soon...)

In version 1.56.0, boost::optional will also implement the emplace() method that I talked about for std::optional. So, let's see that:

#include <boost/optional.hpp>

int main() {
    boost::optional<int> x;
    x.emplace(3);
}

这篇关于使用boost :: optional时避免临时的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！