Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!hplabs!hp-pcd!hplsla!jima
From: jima@hplsla.HP.COM (              Jim Adcock)
Newsgroups: comp.lang.c++
Subject: Re: method selectors
Message-ID: <6590022@hplsla.HP.COM>
Date: 3 Mar 88 22:46:22 GMT
References: <369@trigraph.UUCP>
Organization: HP Lake Stevens, WA
Lines: 30

|The problem is largely one of binding time.  In c++ lexical binding
|occurs very early, in objective-c and even more so in smalltalk, 
|the lexical binding is postponed until runtime.
|
|I like c++ quite a lot, but I can't help feeling that more flexibility
|in choosing the binding time would be very nice.

In general Objective-C binds at the same time a C -- at compile/link time.

However, since Objective-C includes a string representation of the names
of Objective-C methods [equivalent to C++ messages], the Objective-C 
programmer can, with some additional programming, arrange to have the
method selected be completely determined at run time -- at the cost of
doing some additional string searching and hashing.

The equivalent C++ technique would be to use a string representation of a 
virtual function name to find the correct virtual function address in a 
hash table.  Not much harder to do, and has the advantage that you don't
have to keep a string representation of EVERY virtual function name.

Also the Objective-C concept of an "Object" is equivalent to a C++
concept of a pointer to an "Object", so if you don't want to determine
which object a C++ variable refers to until run time, you'll need to
make that C++ variable a pointer or a reference.

In summary, I have found very little difference between C++ and Objective-C
in practical terms on these issues.  The most common difficulties in rewriting
Objective-C programs in C++ is in Objective-C programmers's occasional
use of a C-string as a method selector,  and Objective-C's general lack of type
checking.  Otherwise most Objective-C programming has a one-to-one 
correspondence with C++ programming techniques, and vice versa.