Differences and relationships between static, const, readonly, and static readonly

1. const Modifier

Initialization time:During compilation, the value has been embedded into the code during compilation;

Value status:Dynamic Modification not allowed

Modification Scope: Field, local variable

Main application scenarios: It is mainly used for variable values that do not need to be changed during the program running, such as the mathematical symbol PI;

2. static Modifier

Initialization time: During running, you can assign values when declaring them, or assign values when using constructors or constructors.

Value status: Allowed to be modified

Modification Scope: The class, field, attribute, method, operator, event, and constructor cannot be used for any type other than the indexer, destructor, or class)

Main application scenarios: Mainly applies to the public attributes of the class.

3. readonly Modifier

Initialization time: During runtime, you can assign values during declaration or assign values to constructors in the class.

Value status: Modification allowed, but can only be modified in the constructor

Modification Scope: Field

Main application scenarios: The read-only attribute of the instantiated object.

4. static readonly Modifier

Initialization time: The runtime is a combination of two keywords.

Value status: Modification allowed. Values are assigned during Declaration or in static constructors.

Modification Scope: Field

Main application scenarios: First, compared with const, it is mainly used for reference variables, while const can only be used for string-type reference variables. Second, the read-only public attribute of the class

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