To initialize struct, you can do like this :

public static void main (string[] args) {
    Value val = Value (typeof (int));
    val.set_int (33);
}

But Vala brings another way to initialize values :

public static void main (string[] args) {
    Value val = 33;
}

Your value is initialized with 'int' type and holds '33' int value.

Use one of GLib.Value get methods (see valadoc documentation) or cast your value with the type of your value :

public static void main (string[] args) {
    Value val = 33;
    int i = val.get_int();
    int j = (int)val;
}

Note : if your current value doesn't contain desired type, GObject system will throw critical error :

public static void main (string[] args) {
    Value val = 33;
    string s = (string)val;
}

(process:5725): GLib-GObject-CRITICAL **: g_value_get_string: assertion 'G_VALUE_HOLDS_STRING (value)' failed

This exemple shows how you can pass several types in function parameters :

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 (33);
    print_value (24.46);
    print_value ("string");
}

value-type : gint
value-content : 33

value-type : gdouble
value-content : 24.460000

value-type : gchararray
value-content : "string"

Note : if GObject can transform your value with 'string' type (gchararray), 'strdup_contents' returns converted value, instead of pointer adress

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

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