4.2. Enums and Flags

While C has support for enums, C programmers often do not use enums, opting instead for #defines. Both of these structures can be bound to Vala enums.

This first example is a straight mapping between a C enum and a Vala enum. The C:

typedef enum {
    FOO_A,
    FOO_B,
    FOO_C,
} foo_e;

and the Vala binding:

[CCode (cname = "foo_e", cprefix = "FOO_", has_type_id = false)]
public enum Foo {
    A,
    B,
    C
}

Note how cprefix is used in the above example to prepend FOO_ to all the Vala values when the C is generated.

The second example shows how a series of definitions of constants in C can be mapped to a Vala enum:

#define BAR_X 1
#define BAR_Y 2
#define BAR_Z 3

[CCode (cname = "int", cprefix = "BAR_", has_type_id = false)]
public enum Bar {
    X,
    Y,
    Z
}

Check where the enum is used to determine the correct type, though int and unsigned int are the most common.

There is also a common tendency to use combinable bit patterns. These are convertible to Vala flags enums.

#define FOO_READ (1<<0)
#define FOO_WRITE (1<<1)
#define FOO_CREATE (1<<2)

[CCode (cname = "int", cprefix = "FOO_", has_type_id = false)]
[Flags]
public enum Foo {
    READ,
    WRITE,
    CREATE
}

In Vala, enums and flags may have member functions. In particular, strerr-like functions are best converted to member functions.

Enums may also inherit, so if one set of flags is a superset of another, but they are logically separate, this can be done using inheritance.

#define FOO_A 1
#define FOO_B 2
#define FOO_C 3
#define FOO_D 4
/* takes FOO_A or B only */
void do_something(int);
/* takes any FOO_ value */
void do_something_else(int);

[CCode (cname = "int", cprefix = "FOO_", has_type_id = false)]
public enum Foo { A, B }
[CCode (cname = "int", cprefix = "FOO_", has_type_id = false)]
public enum FooExtended : Foo { C, D }