Re: dynamic binding?

[Sven N. Thommesen]

At 02:27 PM 7/21/1998 GMT, James Marshall wrote:
>Hi,
>  I have a problem when compiling my Swarm app now, because I have 
>two objects each with a method of the same name (but taking 
>and returning different format parameters (ints or doubles). When I 
>try to compile this the compiler warns of the multiple declarations 
>and chooses one to use at compile time. Why does this happen? I 
>though Objective C was supposed to allow polymorphism and dynamic 
>binding? i.e. the method to use should be chosen at run-time, not 
>compile time, after examination and determination of the type of the 
>object receiving the message? 

Well, yes, but that means different object classes are allowed to implement
the same method in different ways -- but 'the same method' means the
different implementations have to define the method interfaces in the exact
same way. I.e., you can have different classes implement '-(int)getData' in
different ways. 

However, objectiveC keeps a single 'database' of method definitions, and it
is a limitation of the language that you are not allowed to have synonymous
methods returning different data types. So if you first define
'-(int)getData', you have an illegal duplicate when you define
'-(double)getData'. (It was probably too much work to build in the
necessary 'magic' to check at runtime for what size the return value is.)

Sorry 'bout that!

Cheers,
--Sven


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