在C ++中奇怪使用[]。发生什么事？ [英] Strange use of [] in C++. What is happening?

问题描述

首先，这不是关于数组或operator []重载的一个虚拟问题！

First of all, this is not a dummy question about arrays or operator[] overload!

我试图编译Qt Creator，但我收到此方法中的错误：

I was trying to compile Qt Creator and I've received an error in this method:

static QList<IDocumentFactory*> getNonEditorDocumentFactories()
{
    return ExtensionSystem::PluginManager::getObjects<IDocumentFactory>(
        [](IDocumentFactory *factory) {
            return !qobject_cast<IEditorFactory *>(factory);
        });
}

错误是：

mainwindow.cpp:748: error: expected primary-expression before ‘[’ token
mainwindow.cpp:748: error: expected primary-expression before ‘]’ token
mainwindow.cpp:748: error: expected primary-expression before ‘*’ token
mainwindow.cpp:748: error: ‘factory’ was not declared in this scope

我知道我做错了编译Qt Creator，可能是g ++版本，但问题不是这样。

I know that I'm doing something wrong to compile Qt Creator, probably g++ version, but the question is not that.

我想理解这段代码，因为对于我这种使用 [] 在语法上不正确。可以有人请解释一下这里发生了什么。

I would like to understand this code because for me this use of [] is syntactically incorrect. Can someone please explain me what is happening here.

推荐答案

这是一个lambda函数。它在C ++ 11中引入。您可以访问 http://en.cppreference.com/w/cpp/language获取更多详情/ lambda 。

That's a lambda function. It was introduced in C++11. You can get more details at http://en.cppreference.com/w/cpp/language/lambda.

如果您不能使用lambda函数，C ++ 03中的等效代码为：

If you are not in a position to use a lambda function, the equivalent code in C++03 would be:

struct MyFunctor
{
   bool operator()(IDocumentFactory *factory) const
   {
      return !qobject_cast<IEditorFactory*>(factory);
   }
};

static QList<IDocumentFactory*> getNonEditorDocumentFactories()
{
    return ExtensionSystem::PluginManager::getObjects<IDocumentFactory>(MyFunctor());
}

你也可以在C ++ 11中使用上面的代码，在c ++ 11中使用lambda函数。

You can use the above in C++11 too but it is more idiomatic to use a lambda function in c++11.

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