Cast the variable to the Value type

[gavr]

My function takes the data and inserts it into the Sqlite table. In order not to create functions to insert for each base type, I decided to accept Value, however, I cannt get a variable of the same type as Value using static or dynamic cast.

void main() {
    Value val = new Value(typeof(string));
    val = "sas";
    var a = val as (val.get_gtype()); //syntax error, expected `unowned'
    var a = (val.get_gtype)val;   //The symbol `val' could not be found
    var a = (string)val;          //works
    print (@"$a");
}

My temporary solution would be:

	string type_check(Value v){
		if (v.holds(typeof (string))) return "s";
		if (v.holds(typeof (int)))    return "i";
		if (v.holds(typeof (uint)))   return "ui";
		if (v.holds(typeof (char)))   return "c";
		if (v.holds(typeof (int64)))  return "i64";
		if (v.holds(typeof (bool)))   return "b";
        ...
	}

But it looks quite so-so, and produces a lot of duplicate code on the receiving side of type_check ().
UPD: Just found out that there is a function type_name() but it’s not much difference

[chrisaw (Chris Williams)]

var is only static type inference; the type is determined at compile time. Typically, you would just make methods with type suffixes (_string, _int64, etc.) because vala does not have function overloading.

Vala does have good support for GVariant though:

void do_something (Variant variant) {
    switch (variant.classify()) {
    case Variant.Class.STRING:
        print ("string %s\n", (string) variant);
        break;
    case Variant.Class.INT32:
        print ("int32 %" + int32.FORMAT + "\n", (int32) variant);
        break;
    default:
        break;
    }
}

void main () {
    do_something ("Hello World");
    do_something (42);
}

As you can see, you still need to dispatch on the type to use the value, but GVariant is serializable, so you could actually store the variant directly in the database.

[gavr]

Ty for answear. I good with thats vala doesnt support func overloading, think its even better, but all this situation looks sad. I already make it like this

public void add(Value data, string tableName=""){
...
        var typeName = data.type_name();
        string val = "";
        switch (typeName) {
            case "gint":      { val = @"$((int)data)";    break;}
            case "gchararray":{ val = quoting((string)data);    break;}
            case "gboolean":  { val = @"$((bool)data)";   break;}
            case "gdouble":   { val = @"$((double)data)"; break;}
            default: error("unknown type");  break;
        }

        query = @"CREATE TABLE IF NOT EXISTS $tableNameFinal (temp);\n" + 
                @"INSERT INTO $tableNameFinal VALUES ($val)";

...

}

[chrisaw (Chris Williams)]

It would be better to use prepared statements instead of building the query as a string.

[jensgeorg]

FWIW, I am doing this in Rygel’s DB layer:

https://gitlab.gnome.org/GNOME/rygel/blob/rygel-0-36/src/librygel-db/database-cursor.vala#L71