Typcasting from a variable?

[timmeh]

This is really basic but I'm unsure on how to do it.

Can I typecast with a variable if I dont know what class the object is going to be?
e.g.

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someMethod(obj : Object; member : Class) begin //set the class of obj to be member obj.Member

or is there some setClass() method for objects?
Would really appreciate knowing how to do this!

[murray]

Usually you will have some idea what class it will be from your design (e.g. it may be one of several subclasses from a common superclass). You can obtain the class of an object by calling the class() method. It is good practice to be as strict as possible with your parameters, as this will help with OO design and with Jade's compile and runtime checking. For example, in your case the parameter could be a superclass type that has the required methods so that typecasting is not necessary. Typecasting to an incompatible class will cause Jade to raise an exception. Also, the lefthand side of any assignment statement must be type compatible with the object it is receiving.

[torrie]

You can type cast a variable, for example:

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someMethod(obj : Object) vars aCustomer : Customer; begin aCustomer := obj.Customer;

If the object is a customer, the code above will work, if not then an exception is thrown at runtime as Murray has pointed out.

You can check whether the object is a customer first e.g.

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someMethod(obj : Object) vars aCustomer : Customer; begin if obj.isKindOf( Customer ) then aCustomer := obj.Customer; else // We do not have a customer. endif;

If you're type casting, then you should consider whether you are better to refactor the code and moving the logic onto a method on the Customer class etc.

However there are some times where it's unavoidable. For example, the display row method on the Table class has the following signature

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displayRow( table: Table input; theSheet: Integer; obj: Object; theRow: Integer; bcontinue: Boolean io): String;

Most people will type case the obj variable in the code. In this case you can however update the signature to match the collection being used, e.g.

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displayRow( table: Table input; theSheet: Integer; customerToDisplay: Customer; theRow: Integer; bcontinue: Boolean io): String;

which then avoids the type casting.