Extended Type Design.

[Bruno Medeiros]

Daniel Keep wrote:
> 
> Bruno Medeiros wrote:
>> Walter Bright wrote:
>>> Bruno has answered your specific questions, so I'll take a more
>>> general tack.
>>>
>>> A symbol is a name to which is 'bound' a value.
>>>
>>> static int x = 3;
>>>
>>> '3' is the value.
>>> 'int' is the type.
>>> 'x' is the symbol.
>>> 'static' is the storage class.
>>>
>>> Here, we bind a new value to the symbol x:
>>>     x = 4;
>>>
>>> A storage class originally meant where the symbol is stored, such as
>>> in the data segment, on the stack, in a register, or in ROM. It's been
>>> generalized a bit since then. The main way to tell a storage class
>>> apart is that:
>>> 1) a storage class applies to the symbol
>>> 2) a type is independent of storage class, i.e. you cannot create a
>>> type that is "pointer to static" or "array of extern". Storage classes
>>> do not affect overloading, nor type deduction.
>>>
>>> 'invariant' and 'const' are type modifiers (aka type constructors),
>>> which mean when they are applied to a type, a new type is created that
>>> is a combination.
>>>
>>> 'invariant' is a guarantee that any data of that type will never
>>> change. 'const' is a guarantee that any data of that type will never
>>> be modified through a reference to that type (though other, non-const
>>> references to that type can modify the data).
>> So 'final' will be a storage class and not a type modifier? That's one
>> of the questions I still have with regards to your design, because I'm
>> not seeing how 'final' can also not-be a type modifier. In particular,
>> again, what is
>>   typeof(&foo)
>> where foo is:
>>   final Foo foo;
>> ?
> 
> I imagine it would be (invariant Foo*): an invariant pointer to a
> reference to a Foo.  Since *no one* is ever allowed to change final
> storage, then a pointer to it must be invariant.
> 
> 	-- Daniel
> 

No, that's not possible. It was mentioned before in another post:
news://news.digitalmars.com:119/etv81l$m94$1@digitalmars.com
Since invariant is (planned to be) transitive, then that typeof can't be 
(invariant Foo*), since the contents of foo can change (altough the 
immediate-value won't).


-- 
Bruno Medeiros - MSc in CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D