c# - 将派生类的对象存储为基类变量。这个的 OOP 术语是什么？

Question

在 C# 中，我们经常使用这样的初始化语法，即基类的实例使用其继承的子类进行初始化:

Control BTN = new Button();

现在我的问题就是，这种初始化的正式名称是什么？

Answer 1

根据 C# 规范，它被称为带有隐式引用转换的简单赋值。

7.16.1 Simple assignment

In a simple assignment, the right operand must be an expression of a type that is implicitly convertible to the type of the left operand.

...

The run-time processing of a simple assignment of the form x = y consists of the following steps:

• ...
• y is evaluated and, if required, converted to the type of x through an implicit conversion (§6.1).

6.1.6 Implicit reference conversions

The implicit reference conversions are:

• ...
• From any class-type S to any class-type T, provided S is derived from T.