6.2. Properties

Vala allows compact classes to have properties, which are syntactic sugar for get and set method pairs. Often C objects with opaque implementations will provide a collection of functions to query state about the instance. These can be converted to properties given the following:

  • The get method has the signature T get(I self) and the set method has the signature void set(I self, T val). They need not actually occur in pairs.

  • The get method does not have side effects that are not obvious to the user.

  • The get method is cheap to call.

  • The set method does not have error information being returned.

Unlike most return types, the return of a get method is assumed to be unowned unless explicitly owned.

Consider:

typedef struct foo Foo;
int foo_item_count(Foo f);
int foo_max_items(Foo f);
void foo_set_max_items(Foo f);

public class Foo {
    public int item_count {
        [CCode (cname = "foo_item_count")] get;
    }
    public int max_items {
        [CCode (cname = "foo_max_items")] get;
        [CCode (cname = "foo_set_max_items")] set;
    }
}

All the usual CCode attributes may be applied to get; and set; and owned may be applied to change the default ownership of get;. Note that changing the ownership of the property is the wrong thing to do unless the instance doesn’t actually own the value provided to it by set;.