Question

i’d like to throw an argument error if a particular function doesn’t work without a passed value that also happens to be a public constant of the class containing the function.

is there anyway to determine if a class owns a public constant instead of having to iterate thru all of them?

something like this:

public static const HALIFAX:String = "halifax";
public static const MONTREAL:String = "montreal";
public static const TORONTO:String = "toronto";

private var cityProperty:String;

public function set city(value:String):void
     {
     if (!this.hasConstant(value))
        throw new ArgumentError("set city value is not applicable.");

     cityProperty = value;
     }

public function get city():Strig
     {
     return cityProperty;
     }

currently, for this functionality i have to write the city setter function like this:

public function set city(value:String):void
     {
     if (value != HALIFAX && value != MONTREAL && value != TORONTO)
        throw new ArgumentError("set city value is not applicable.");

     cityProperty = value;
     }

is this the only way to accomplish this task?

Answer 1

Yes, if you use reflections:

private var type:Class;
private var description:XML;

private function hasConstant (str : String ) : Boolean 
{
    if (description == null) 
    {
        type = getDefinitionByName (getQualifiedClassName (this)) as Class;
        description = describeType (type);      
    }
    for each ( var constant:XML in description.constant) 
    {
        if (type[constant.@name] == str) return true;
    }
    return false;
}

Note that for this to work, all constants must always be String objects declared public static const.