[Pharo-dev] Smalltalk = strongly typed

kilon thekilon at yahoo.co.uk
Sat Aug 3 06:49:49 EDT 2013


"
Smalltalk has types: a set of objects and the messages they understand"

Nope thats not what a type is. A type is a category of data.

Its that simple. Your set of objects and the messages they understand can do
thousands of things. Emulating types is one of those things. 

Also what happens in implementation is not related to language.
Implementation is one thing language is another.

Also even if you see it philosophical still is very clear. Types in the end
is a set of restrictions which tells "I am the language and I wont allow you
to shoot yourself on the foot. I know better." Smalltalk on the other hand
begs you "Hack me dude, hack me!". 

Smalltalk does not enforce such restrictions. But then it does not prevent
you from implementing such restrictions. Afterall a static typed language
does not prevents from implementing dynamic types. If it did it would be
impossible to use C to create python or smalltalk.

With any language there are a billion ways to skin a cat. What it differs is
the things they offer out of the box
.Nothing is set in stone.


Carla F. Griggio wrote
> Well, I've always defined a type as the a set of values and the operations
> you can do with them. For example, the set of values { 1, 2, 3, 4, ... }
> and the operations { + , - , * , ... } would be the type Integer. With
> that
> in mind, *Smalltalk has types: a set of objects and the messages they
> understand*. And thanks to polymorphism a type *is not* a synonym of a
> class, as instances of different objects can understand messages in
> common.
> So yes, "everything is an object" beacuse all objects are instances of a
> class that inherits from Object, but from my point of view it's not true
> that all objects are of one same type.
> 
> Everytime an object doesn't understand a message is telling you that
> you're
> doing an operation on the wrong type of object.
> 
> As some others have already said, I don't like the terms "strongly typed"
> or "weakly typed" because sometimes is ambiguous, and I rather say
> this: *Smalltalk
> has dynamic type-checking in runtime* (instead of compilation time),
> because it checks if an object can perform the operation you want (the
> message) in the moment of executing that operation (when you send the
> message).
> 
> Now, talking not-so-siriously, and maybe I'm getting a little
> code-philosofical here... If we take into account what I've just defined
> as
> a type, and knowing that all objects are instances of a class that
> inherits
> from Object, I think the term "unityped" should actually be replaced for
> "multityped", as the same object could respond to many different types
> depending on the interface its client wants it to understand. But that
> happens maybe in any object-oriented program, the thing is that in
> Smalltalk it's very natural and you don't even have to think about it (in
> Java you would have to explicitly use 'interfaces').
> 
> 
> 
> 
> 
> On Sat, Aug 3, 2013 at 4:02 AM, Hernán Morales Durand <

> hernan.morales@

>> wrote:
> 
>> That is correct, there are no types in Smalltalk.
>> Cheers,
>>
>> Hernán
>>
>> El 02/08/2013 15:55, Igor Stasenko escribió:
>>
>>  I wonder if 'types' can be applied to smalltalk at all.
>>> Saying it is 'unityped' language (since everything is an object) is
>>> same as saying it has no types.
>>>
>>> Because where you need types? When you want to manipulate with data,
>>> but in smalltalk all
>>> data manipulation semantics is provided and implemented at primitive
>>> level, but not by the language itself.
>>> At language level the only semantics which is defined is message
>>> passing, closures,
>>> return and assignment.
>>>
>>> There is no any rule(s), in smalltalk at language level, saying that
>>> result of expression:
>>>
>>> 1 + 2
>>>
>>> should be of integer type. Because this is provided by implementation
>>> but not defined by language itself e.g.:
>>> it is just a method in corresponding class, which implemented in such
>>> a way that result of expression will be instance of Integer (or
>>> SmallInteger to be precise).
>>> Now, if you change implementation so result will be float (or anything
>>> else), will such change allow you to say, that it is no longer
>>> smalltalk, or that now it is weakly typed or "anything-else typed"?
>>>
>>> Because smalltalk code do not operates directly with data, but only
>>> with references to it (which is objects).
>>>
>>> Take an assignment, for example.
>>> In staticly-typed language assignment copies the value of expression
>>> to variable, e.g.:
>>>
>>> a = 10
>>>
>>> "now variable a has value = 10"
>>>
>>> in smalltalk, assignment is not copying value, but changing the
>>> reference:
>>>
>>> a := 10
>>>
>>> "now variable a points (or refers) to object '10'"
>>>
>>> and thus, whatever 'type' used to represent the integer value 10 is
>>> completely irrelevant
>>> for assignment operation.
>>>
>>>
>>
>>





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