如何立即调用C ++ lambda？ [英] How to immediately invoke a C++ lambda?

问题描述

我正在继承的类中的构造函数要求传递一个非平凡的对象。类似于此：

A constructor from a class I'm inheriting requires a non-trivial object to be passed in. Similar to this:

MyFoo::MyFoo() : SomeBase( complexstuff )
{
    return;
}

复杂物具有与 MyFoo 几乎没有关系，所以我不想将其传递出去。

The complexstuff has little to do with MyFoo, so I didn't want to have to pass it in.

而不是编写某种类型的1-off临时函数返回 complexstuff 我使用了lambda。我花了几分钟才弄清楚我必须调用该lambda。所以我的代码现在看起来像这样：

Instead of writing some kind of 1-off temporary function that returns complexstuff I used a lambda. What took me a few minutes to figure out is I have to invoke the lambda. So my code now looks like this:

MyFoo::MyFoo() : SomeBase(
    []()
    {
        /* blah blah do stuff with complexstuff */
        return complexstuff;
    } () )
{
    return;
}

如果您没有抓住它，那就太微妙了。但是在lambda主体之后，我不得不放入（）来告诉编译器立即运行 lambda。在我弄清楚自己做错了什么之后，这才有意义。否则，如果没有（）来调用lambda，gcc会说类似以下内容：

If you didn't catch it, it is subtle. But after the lambda body, I had to put () to tell the compiler to immediately "run" the lambda. Which made sense after I figured out what I had done wrong. Otherwise, without the () to invoke the lambda, gcc says something similar to this:

error: no matching function for call to 'SomeBase(<lambda()>)'

但是现在我在想-我正确地做到了吗？在C ++ 11或C ++ 14中，是否有更好的方法告诉编译器我希望它立即调用我编写的lambda？还是像我惯常的那样添加空的（）？

But now that has me thinking -- did I do this correctly? Is there a better way in C++11 or C++14 to tell the compiler that I want it to immediately invoke a lambda I've written? Or is appending an empty () like I did the usual way to do this?

推荐答案

但是现在我在想-我正确地做到了吗？

But now that has me thinking -- did I do this correctly?

是

在C ++ 11或C ++ 14中是否有更好的方法告诉编译器我希望它立即生效调用我编写的lambda吗？

Is there a better way in C++11 or C++14 to tell the compiler that I want it to immediately invoke a lambda I've written?

我不知道。 Lambda也是一个函数对象，因此您需要要有一个（）来调用它，没有办法解决（除了当然，某些函数会调用lambda，例如 std :: invoke ）。

Not that I know of. A lambda is also just a function object, so you need to have a () to call it, there is no way around it (except of course some function that invokes the lambda like std::invoke).

如果需要，可以删除（），因为您的lambda不接受任何参数。

If you want you can drop the () after the capture list, because your lambda doesn't take any parameters.

或者像我惯常的那样添加空的（）这是

是的，这是最短的方法。如前所述， std :: invoke 也可以代替，但需要更多的输入。我想说直接使用（）进行调用是常见的方法。

Yes, it is the shortest way. As said before, std::invoke would also work instead, but it requires more typing. I would say a direct call with () is the usual way it is done.

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