std :: optional和多态 [英] std::optional and polymorphism

问题描述

我在许多文章中都读过Stack Overflow，它说到使用指针(用于参数或返回值)并且允许使用nullptr(使其成为可选)时，通常最好使用std::optional.

I have read on Stack Overflow in many posts that when pointer is used (for argument or return value) and nullptr is allowed (making it optional), it is generally better to use std::optional instead.

但是如果指针指向多态类型怎么办?最好使用std::optional还是指针?

However what if the pointer refers to polymorphic type? Is it best to use std::optional or a pointer?

推荐答案

optional不适用于多态类型.这是一个值类型，多态基类在optional中不起作用.就像将多态基类放入vector或类似容器中一样.

optional doesn't work with polymorphic types. It's a value type, and polymorphic base classes don't work in an optional. Just as putting polymorphic base classes in vector or similar containers doesn't work.

返回一个指针.建议通常被称为一般"是有原因的.

Return a pointer. There's a reason why the advice is usually stated as "generally".

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