Extended Type Design.

[Daniel Keep]

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

-- 
int getRandomNumber()
{
    return 4; // chosen by fair dice roll.
              // guaranteed to be random.
}

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