I think it's also important here that Clojure methods are actual Java
methods - Clojure likes to stay close to the host functionality. A map
with a function isn't a class with a method because the JVM bytecode
doesn't let you invoke it that way directly. A Clojure function is not
a method because methods are not first class, it's an Object with a
static .invoke method (and some other details that are less important
here).
This object as hash with functions model is useful for learning (and
there's a lot of scheme and common lisp code that actually works this
way). With some effort, you can do everything with a function in a map
that you can with an object with a method if you are careful to
provide the object of the first arg.
But it's normal in Clojure to use the built in affordances. For real
code, defrecord gives you a new class that operates in a way similar
to this but with lower friction to the underlying bytecode (it
implements actual methods but also acts like a hash map for its
fields). Protocols let you use a hash map for extension (they act like
interfaces for classes, but you can add new implementations
dynamically, letting you do what you would do by adding a function
under a key on a hash, but tracking it on the protocol side).
On Tue, Mar 31, 2020 at 7:39 AM Jason Felice <jason.m.fel...@gmail.com> wrote:
>
> A subtle difference between a map of functions and a Python class is that the
> class has implicit "self" or "this". Otherwise, these are semantically the
> same. Well, ignoring that Clojure maps are immutable.
>
> In fact, C++ compilers compile methods by inserting a first "this" argument
> and mangling the name. Virtual methods (ones which can be overridden) are
> collected into what is effectively a map attached to the instance.
>
> On Tue, Mar 31, 2020 at 4:41 AM Dieter Van Eessen
> <dieter.van.ees...@gmail.com> wrote:
>>
>> Hello,
>>
>> I've got a clojure and a python piece of code. Both seem to create what can
>> be considered an instance of a class. Wherein lies the conceptual difference?
>>
>> Python:
>> class MYCLASS():
>> def __init__(self, x):
>> self.x = x
>> def MYMETHOD(self):
>> ...
>>
>> def MYFUNCTION():
>> lol = MYCLASS()
>>
>> Clojure:
>> (defn MYCLASS [x]
>> {:x [x]
>> :MYMETHOD (fn [] (MYCLASS ...))})
>>
>> (let [lol (MYCLASS ...)])
>>
>> I know its not valid code, but I hope you see what I'm aiming at: isn't
>> using a map with functions in it just the same as a class?
>> Or is only the user interface of the language conceptually equal, while the
>> underlying plumbing is completely different?
>> If this is the case, wherein lies the major differences?
>>
>> If one could simply point me in the right direction, I'd already be very
>> pleased. Most literature I've read so far only explains clojure can be used
>> this way, but never focuses deeper on the subject.
>>
>> kind regards,
>> Dieter
>>
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