在 c# 中声明一个类时可以拥有的最大有效修饰符数量是多少？

Question

This question is more for curiosity.

By modifiers I mean, keywords that you add before declaring a class.

eg

//1       2        3             
public abstract partial class Foo
{

}

This have 3 modifiers public , abstract , and partial .

Zero modifiers, in this question perspective, would be something like

class Foo
{

}

What is the max number of valid modifiers you can have before the name of the class when declaring it?

Answer 1

The maximum number is...

5!

(or 6 if you count unsafe )

According to here , a class declaration looks like this:

class_declaration
    : attributes? class_modifier* 'partial'? 'class' identifier type_parameter_list?
      class_base? type_parameter_constraints_clause* class_body ';'?
    ;

You probably don't count the attributes as "modifiers", but you probably would count the partial keyword as a "class modifier", though it is not an actual class_modifier .

The list of class_modifier is:

class_modifier
    : 'new'
    | 'public'
    | 'protected'
    | 'internal'
    | 'private'
    | 'abstract'
    | 'sealed'
    | 'static'
    | class_modifier_unsafe
    ;

We know the longest access modifier is protected internal , so we can ignore all the access modifiers:

class_modifier
    : 'new'
    | 'abstract'
    | 'sealed'
    | 'static'
    | class_modifier_unsafe
    ;

You can only choose one of sealed , static and abstract , so we are left with 6 "keywords":

• protected
• internal
• new
• sealed / static / abstract
• partial
• unsafe

Note that new and protected internal can only be used in nested class declarations.