Extended Type Design.

[Andrei Alexandrescu (See Website For Email)]

Sean Kelly wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> Don Clugston wrote:
>>> Assuming that 'invariant' = really constant, 'const' = C++ 
>>> pseudo-const...
>>
>> Yah.
>>
>>> It's better than super const. However:
>>> (1) I would want to go through all my existing D code and change 100% 
>>> of my usages of 'const' to 'invariant'.
>>
>> Great to hear that!
> 
> Great perhaps, but it does suggest that 'const' should perhaps be the 
> signifier for what 'invariant' has been proposed for (the literal 
> meaning of each term notwithstanding)?

No. There will be far more uses for const than for invariant. You can 
take my word for that.

>>> (2) although (1) could be avoided with the rule that 'const' on a 
>>> declaration implicitly means 'invariant', this would then mean that 
>>> to match a 'const' value, you use 'invariant'; but to match a 
>>> non-const value, you use 'const'. That's horribly confusing.
>>
>> This I don't understand. Could you give an example?
> 
> invariant int* x;
> int* y;
> 
> void fn( const int* z ) {}
> 
> fn( x );
> fn( y );
> 
> Assuming the above is legal, 'const' is the qualifier which binds to all 
> reference types, ie. "to match a non-const value, you use 'const'."

That is correct.


Andrei