What the recommended way now to create an instance and override its methods?

[Hussein B.]

Hi,

I know we usually use 'proxy' macro when we want to create an instance of a concrete class and override some of its methods. But do we have now a recommended approach?  

AFAIK, reify only works with protocols and interfaces, can't be used to create an instance and override its methods.

I'm a little bit worry about 'proxy' macros since some devs are saying that it has a performance penalty.

Thanks for help and time.

[Jim]

On 18/06/13 08:45, Hussein B. wrote:
> I know we usually use 'proxy' macro when we want to create an instance
> of a concrete class and override some of its methods. But do we have
> now a recommended approach?

'proxy' is the recommended approach unless you have some weird
overriding requirements like providing an override based on the type of
the arguments rather than the arity, in which case you have to drop to
Java and manually construct your proxy...

yes, 'reify' will be slightly faster but as you say it only works with
abstractions and not concrete objects.

hope that helps, :)

Jim

[Hussein B.]

Since reify allows us to override methods of an object, it is better to do:

(def meh-object (MehClass.))

(reify meh-object

  ;; override methods)

than:

(proxy MehClass[]

  ;; override methods)

Thanks.

[Jim]

On 18/06/13 12:34, Hussein B. wrote:

Since reify allows us to override methods of an object, it is better to do:

'reify' allows you to implement/satisfy interface-methods - not to override concrete ones.

user=> (reify String
  #_=>  (length [this] (count this)))

user=> CompilerException java.lang.IllegalArgumentException: only interfaces are supported, had: java.lang.String, compiling:(NO_SOURCE_PATH:1:1)

Jim

[Hussein B.]

Hmm,

then why Clojure docs http://clojuredocs.org/clojure_core/clojure.core/reify mentions 'object':

protocol-or-interface-or-Object
(methodName [args+] body)*

[Cedric Greevey]

That's the *class* Object, with a capital O. It's the one concrete class that can be extended and its methods overridden using reify (or deftype).

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[Jim]

as Cedric pointed out, it means the java.lang.Object class...not any object

Jim

[Gary Trakhman]

I think you need to read something comprehensive before any of these replies start to make sense, I would recommend Joy Of Clojure, or some good blog posts.

This might be a good starting point with some links for further reading:

http://tech.puredanger.com/2011/08/12/subclassing-in-clojure/

To understand the issues fully will take a little effort.

On Tue, Jun 18, 2013 at 7:43 AM, Hussein B. <hubag...@gmail.com> wrote:

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