[Pharo-dev] what is the new way to do Smalltalk at: #MyClass?

Camille Teruel camille.teruel at gmail.com
Mon Aug 26 06:31:41 EDT 2013


On 26 août 2013, at 10:56, Esteban Lorenzano wrote:

> 
> On Aug 25, 2013, at 9:40 AM, Camille Teruel <camille.teruel at gmail.com> wrote:
> 
>> 
>> On 24 août 2013, at 19:20, Camillo Bruni wrote:
>> 
>>> We have now:
>>> 
>>> String >> #asClass
>>> String >> #asClassIfAbsent:
>>> String >> #asClassIfPresent:
>> 
>> I don't understand why we need this new way.
>> Is it just to avoid calling 'Smalltalk globals at: #MyClass'?
> 
> exactly
> 
>> Because these names are confusing, and the 'as' prefix suggests a conversion while it's an access (with indirection but still a mere access).
>> And #asClass has no sender.
>> If you think 'Smalltalk globals at: #MyClass' is really too long to type, lets just create a new global ThisEnvironment := Smalltalk globals.
> 
> this was already discussed. With #asClass and relatives what you have is a better abstraction jut because you are decoupled of "Smalltalk globals", it is not a big win now, but it open doors to better designs with environments, etc. 
> At least, that was my understanding when the issue arise at the beginning.

It's not a better abstraction, it's a worse one. 
Sending #asClass to a symbol will ever execute the same method that anyway as to rely on a global: Smalltalk.
And this global is solved in only one environment: the one of the class Symbol where #asClass and co. are implemented.
So if you want separated environments you know what kind of thing you'll end up writing?

'#Foo asClassInEnvitonment: self class environment'

or implementing:

Symbol>>#asClass
	^ self asClassInEnvironment: thisContext sender receiver class environment

However, as soon as the compiler use the environment of the compiled method's class to solves the globals it contains, Smalltalk can refer to anything.
So the only problem with: 'Smalltalk globals at:'  is that you send a message #globals to the global Smalltalk to fetch the environment while we could just have a global ThisEnvironment pointing to itself. 

Writting 'ThisEnvironment at: #Foo' is much more natural.

If we want separated environments, each environment just have to define a binding ThisEnvironment pointing to itself and everything works well.
What I don't like with #asClass and co. is the style: you talk to a symbol instead of an environment. 
It's like saying: '#key valueIn: aDict' instead of: 'aDict at: #key', 'letter beSentBy: postman to: receiver' instead of: 'postman send: letter to: receiver', etc...

In Smalltalk we already have self to refer to the current receiver and thisContext to refer to the current stack frame. If we want different environments, is it that weird to have a ThisEnvironment to refer to the current environment?

> 
> Esteban 
> 
>> 
>> 
>>> 
>>> On 2013-08-24, at 17:55, Fernando Olivero <fernando.olivero at usi.ch> wrote:
>>>> I prefer to evaluate
>>>> 
>>>> Smalltalk globals classNamed: #MyClass
>>>> 
>>>> Fernando
>>>> 
>>>> On Sat, Aug 24, 2013 at 11:57 AM, Stéphane Ducasse
>>>> <stephane.ducasse at inria.fr> wrote:
>>>>> 
>>>>> Is it
>>>>> 
>>>>> asClass?
>>>>> 
>>>>> Stef
>>>>> 
>>>> 
>>> 
>>> 
>> 
>> 
> 
> 





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