The typedef keyword is used to declare an identifier as an alias for an existing type. Like all D type declarations, the typedef keyword is used outside probe clauses in a declaration of the form:

typedef existing-type new-type ;

where existing-type is any type declaration and new-type is an identifier to be used as the alias for this type. For example, the declaration:

typedef unsigned char uint8_t;

is used internally by the D compiler to create the uint8_t type alias. Type aliases can be used anywhere that a normal type can be used, such as the type of a variable or associative array value or tuple member. You can also combine typedef with more elaborate declarations such as the definition of a new struct:

typedef struct foo {
	int x;
	int y;
} foo_t;

In this example, struct foo is defined as the same type as its alias, foo_t. Solaris C system headers often use the suffix _t to denote a typedef alias.