Fwd: Class double-bind

Jason Orendorff jason.orendorff at gmail.com
Wed Mar 4 12:21:42 UTC 2015

Oops, accidentally sent this only to Allen.

---------- Forwarded message ----------
From: Jason Orendorff <jason.orendorff at gmail.com>
Date: Tue, Mar 3, 2015 at 11:34 AM
Subject: Re: Class double-bind
To: Allen Wirfs-Brock <allen at wirfs-brock.com>

On Mon, Mar 2, 2015 at 5:54 PM, Allen Wirfs-Brock <allen at wirfs-brock.com> wrote:
>  Pretty much everyone I've seen discover the function binding equivalent  (or have it explained to them for the first time) was shocked.  What! 'function fact(n) {return n>1? n*fact(n-1):1}' doesn't necessarily recur on the same function?  that's crazy! is the typical reaction.

Perhaps this is a little overstated? In Scheme, Python, Lua, Ruby, and
Smalltalk, code in a function/class/method that refer to it by name
refer to the external binding. That binding is mutable in all those
languages except Ruby and Smalltalk (and even in those, I think you
*can* mutate it, but the language discourages it).

So basically every language in this space has the same behavior. JS
differs only in that it has a named-function-expression syntax, which
I think the others lack.

I can't think of a language where two bindings are created and they
can then diverge. This is novel weirdness.

> Similarly, it would be crazy if:
>   class Foo {
>       static makeFoo() {return new Foo}
>   }
> didn't give you a factory method that created instances of Foo.

Well, you're calling every existing dynamic language with classes
crazy. I don't think that's very useful.

>> If we wanted classes to be tamper-proof, then the outer binding would
>> be immutable as well. It's not; it's mutable; yet every use case I can
>> think of for actually assigning to it is silently broken due to the
>> double binding.
> We needed global class bindings to be replaceable.

That makes sense.


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