constness for arrays

[Andrew Fedoniouk]

Dynamic constness versus static (compile time) constness is not new.

For example in Ruby you can dynamicly declare object/array readonly and
its runtime will control all modifications and note - in full as Ruby's 
sandbox
(as any other VM based runtime) has all facilities to fully control
immutability of such objects.

In case of runtimes like D (natively compileable) such control is not an
option.

I beleive that proposed runtime flag a) is not a constness in any sense
b) does not solve compile verification of readonlyness and
c) can be implemented now by defining:
struct vector
{
    bool readonly;
    T*  data;
    uint length;
}

Declarative contness prevents data misuse at compile time
when runtime constness moves problem into execution time
when is a) too late to do anything and b) expensive.

I would mention old idea again - real solution would be in creating of
mechanism of disabling exiting or creating new opertaions
for intrinsic types.

For example string definition might look like as:

typedef  string char[]
{
    disable opAssign;
    ....
    char[] tolower() { ..... }
}

In any case such mechanism a) is more universal than const in C++
b) allows to create flexible type systems and finally
c) this will also legalize situation with
"external methods" D has now for array types.

The later one alone is a good enough motivation to do so
as current situation with "external methods" looks like as
just a bug of design or compiler to be honest.

I am yet silent that it will make D's type system unique
in this respect among other languages.

Andrew Fedoniouk.
http://terrainformatica.com