Re: OT: Categories and alloc.
Re: OT: Categories and alloc.
- Subject: Re: OT: Categories and alloc.
- From: mmalcolm crawford <email@hidden>
- Date: Sat, 29 Jun 2002 21:42:59 -0700
On Friday, June 28, 2002, at 01:20 PM, Michael Gersten wrote:
The problem: Objective C and Java both allow protocols/interfaces to
specify what you can do with an object. Anything that is written to an
interface specification will work with any object that implements that
specification, and can work with any class that does so.
But how does it get something of that interface type?
You must create an instance of a specific class. Protocols and
interfaces simply define a collection of methods. They do not specify
anything else, such as the implementation of the methods, instance
variables the object might have, what superclasses the object might have
etc.
You can declare a variable as being of type a given protocol/interface:
NSCoding *myCodableObject;
But it has occurred to me that even if you had all that, you'd still
have a problem. Allocation.
As implied above, you must create an instance of a class that conforms
to the relevant protocol / implements the relevant interface:
myCodableObject = [[NSMutableSet alloc] init];
or
myCodableObject = [[NSString alloc] initWithCString:"hello"];
or
myCodableObject = [NSDate date];
etc.
mmalc
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