Question

In C#, we often use a initializing syntax that a instance of a base class is initializing with its inherited child class like this:

Control BTN = new Button();

Now my question is just that, what is the formal name of this kind of initializing?

Answer 1

According to the C# specification, it is called simple assignment with an implicit reference conversion.

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.