C++ Weekly - Episode 149 脱水版: C++20's Lambda Usability Changes

C++20 Lambda 实用性的改变

1. C++20 Lambda 具有默认构造函数

   auto l = [] { return 5; };
   decltype(l) new_lambda;

该块代码在 C++17 会提示编译错误, 无匹配的构造函数:

error: no matching constructor for initialization of 'decltype(l)' (aka '(lambda at :11:13)')

2. C++20 Lambda 允许赋值操作

   auto l = [] { return 5; };
   auto m = l;

   l = m;

该块代码在 C++17 会提示编译错误, 拷贝赋值操作被标记成 delete

error: object of type '(lambda at :11:13)' cannot be assigned because its copy assignment operator is implicitly deleted

3. C++20 支持未经求值的 lambda 表达式

   decltype([]{}) n;

该块代码在 C++17 会提示编译错误, Lambda 表达式处于未经求的表达式

error: lambda expression in an unevaluated operand