From: brucehoult@pobox.com (Bruce Hoult)
Newsgroups: comp.lang.dylan
Subject: Re: make() and initialize()?
Date: Mon, 22 May 2000 12:53:55 +1200
Lines: 38
Message-ID: <brucehoult-2205001253550001@bruce.bgh>
References: <200005211856.OAA21139@life.ai.mit.edu>

In article <200005211856.OAA21139@life.ai.mit.edu>, Nolan Darilek
<nolan_d@bigfoot.com> wrote:

> I've finally encountered a situation in which I'd like to override the
> default/generated constructors. I've seen code which overrides make,
> and code which overrides initialize on the new class. What is the
> difference between make() and initialize()?

Are you familiar with C++?  It's the same as the difference between
"operator new" and the constructor.

make() ("operator new" in C++) finds some memory space to put the new
object in.  initialize() (the constructor in C++) puts some sensible
initial values into that memory space.


You write your own initialize() if you want to do things that can't be
done with init-value, init-expression, init-function.  Which basically
means (I think) things that need to set up more than one slot in some
pattern.

You write your own make() if you want to:

- substitute a different sort of object than the user asked for e.g.
make(<vector>) actually returns a <simple-object-vector>.  This is the
"factory method pattern" in C++ or Java.

- return an existing object instead of a new one.  e.g. from a cache or
free-list or maybe something like the "Fly-weight Pattern".



The place the Dylan/C++ analogy breaks down is that in C++ the constructor
is always run after operator new, but in Dylan if you write yoru own
make() then you don't have to call initialize() (which is handy if you're
returning an existing object)

-- Bruce