vala Using GLib.Value Register types for GLib.Value

Example

In previous example, Value.strdup_contents prints GLib.DateTime as pointer address. You can register functions that will transform value to desired type. First, create a function that will have this signature :

static void datetime_to_string (Value src_value, ref Value dest_value) {
    DateTime dt = (DateTime)src_value;
    dest_value.set_string (dt.to_string());
}

then register this function with Value.register_transform_func :

Value.register_transform_func (typeof (DateTime), typeof (string), datetime_to_string);

now GObject can convert any DateTime object to string value.

the complete example :

static void datetime_to_string (Value src_value, ref Value dest_value) {
    DateTime dt = (DateTime)src_value;
    dest_value.set_string (dt.to_string());
}

static void print_value (Value val) {
    print ("value-type : %s\n", val.type().name());
    print ("value-content : %s\n\n", val.strdup_contents());
}

public static void main (string[] args) {
    print_value (new DateTime.now_local());
    Value.register_transform_func (typeof (DateTime), typeof (string), datetime_to_string);
    print_value (new DateTime.now_local());
}

value-type : GDateTime
value-content : ((GDateTime*) 0x560337def040)

value-type : GDateTime
value-content : 2017-04-20T18:40:20+0200