Partial types

A type declaration can be split across multiple partial type declarations. The type declaration is constructed from its parts by following the rules in this section, whereupon it is treated as a single declaration during the remainder of the compile-time and run-time processing of the program.

A class-declaration, struct-declaration or interface-declaration represents a partial type declaration if it includes a partial modifier. partial is not a keyword, and only acts as a modifier if it appears immediately before one of the keywords class, struct or interface in a type declaration, or before the type void in a method declaration. In other contexts it can be used as a normal identifier.

Each part of a partial type declaration must include a partial modifier. It must have the same name and be declared in the same namespace or type declaration as the other parts. The partial modifier indicates that additional parts of the type declaration may exist elsewhere, but the existence of such additional parts is not a requirement; it is valid for a type with a single declaration to include the partial modifier.

All parts of a partial type must be compiled together such that the parts can be merged at compile-time into a single type declaration. Partial types specifically do not allow already compiled types to be extended.

Nested types may be declared in multiple parts by using the partial modifier. Typically, the containing type is declared using partial as well, and each part of the nested type is declared in a different part of the containing type.

The partial modifier is not permitted on delegate or enum declarations.