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From: stt@inmet.inmet.com
Newsgroups: comp.compilers
Subject: Re: Defining polymorphism vs. overloading
Keywords: polymorphism
Message-ID: <19400003@inmet>
Date: 15 Sep 90 14:32:00 GMT
Sender: compilers-sender@esegue.segue.boston.ma.us
Reply-To: stt@inmet.inmet.com
Organization: Compilers Central
Lines: 34
Approved: compilers@esegue.segue.boston.ma.us

Here is my favorite so far:

> - Overloading is the ability to have the same name (symbol) attached
> to different entities (functions, procedures, variables or whatsoever).
> 
> - Polymorphism is the ability to have the compiler decide *at runtime*
> which entity to use depending on the runtime type (class or whatever)
> of the contents of variables.
> 
> - Generic code is a chunk of code that has the ability of performing
> the same algorithm with more than one type. The actual types may be
> known at runtime (as in Smalltalk) or at compile time (as in Ada).
> . . .
> Joaquim Manuel Soares Baptista, aka px@fctunl.rccn.pt, px@unl.uucp

However, I would revise the definition of polymorphism as follows:

- Polymorphism is the ability to have a single entity (usually a parameter or
a pointer) refer to objects/values of more than one type.  Run-time
polymorphism (like C++) allows the dispatch to type-specific code to be made
at run-time.  Compile-time polymorphism (like Ada's generics) performs the
"dispatch" to type-specific code at compile-time.

- Generic code is code that manipulates polymorphic parameters/pointers, by
taking advantage of the commonality across the multiple types represented by
them.  In most cases, however, it must eventually "dispatch" to type-specific
code.

S. Tucker Taft    stt@inmet.inmet.com;  uunet!inmet!stt
Intermetrics, Inc.
Cambridge, MA  02138
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