return{}的含义 - C++11新特性

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  之前有小伙伴在刷题过程中，遇到 return{} 懵逼了，其实这个是C++11的新特性，本文将介绍return{}的用法，如果有不足欢迎大佬斧正（＞人＜；）~
  我们先来看看比较官方的details

• If the braced-init-list is empty and T is a class type with a default constructor, value-initialization is performed.

• Otherwise, if T is an aggregate type, aggregate initialization is performed.

• Otherwise, if T is a specialization of std::initializer_list, the T object is direct-initialized or copy-initialized, depending on
  context, from the braced-init-list.

• Otherwise, the constructors of T are considered, in two phases:
   - All constructors that take std::initializer_list as the only
  argument, or as the first argument if the remaining arguments have
  default values, are examined, and matched by overload resolution
  against a single argument of type std::initializer_list
   - If the previous stage does not produce a match, all constructors of T
  participate in overload resolution against the set of arguments that
  consists of the elements of the braced-init-list, with the restriction
  that only non-narrowing conversions are allowed. If this stage
  produces an explicit constructor as the best match for a
  copy-list-initialization, compilation fails (note, in simple
  copy-initialization, explicit constructors are not considered at all).

• Otherwise (if T is not a class type), if the braced-init-list has only one element and either T isn’t a reference type or is a reference
  type that is compatible with the type of the element, T is
  direct-initialized (in direct-list-initialization) or copy-initialized
  (in copy-list-initialization), except that narrowing conversions are
  not allowed.

• Otherwise, if T is a reference type that isn’t compatible with the type of the element. (this fails if the reference is a non-const
  lvalue reference)

• Otherwise, if the braced-init-list has no elements, T is value-initialized.

  看了解释后，归结就是 “返回用大括弧初始化的该函数对象（返回的类型和函数类型一样）” 举个例子后就能明白了
在C++11之前, 你想返回一个string的函数，你可能会这样写：

string get_string() {return string();
}

在C++11之后，可以这样写：

std::string get_string() {return {};   // 即返回这个函数所构造出来的对象
}这里再举个例子：
vector<int> twoSum(vector<int>& nums, int target) {//...经过一系列操作后构造好了nums这个vector数组if(target > 10) return {};       //返回一个空的vector<int>对象else if(target < 5) return nums;    //直接返回nums作为对象else return {1, 2, 3};    //直接构造好vector<int>并将这个对象返回
}

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