Re: Unconstrained Arrays

[Jeffrey Creem <jeff@thecreems.com>]

belteshazzar wrote:
> On Mar 17, 11:49 am, "Jeffrey R. Carter"
> <spam.jrcarter....@spam.acm.org> wrote:
>> belteshazzar wrote:
>>> I have a program that uses a lot of different sized arrays and passed
>>> into math functions. So I'm using an unconstrained array type. The
>>> problem that I have is that I'm not allowed to use "new" this means
>>> that I have to use pools (which I can't because to intantiate a pool I
>>> have to constrain the array type) or allocated the arrays on the
>>> stack. Allocating the arrays on the stack is fine, BUT it means that i
>>> have to use array initializers so that they remain unconstrained
>>> rather than becoming an anonomous contrained type that can no longer
>>> be passed to my math functions.
>> I'm not clear what you're talking about. You can pass a constrained subtype to a
>> subprogram that takes a parameter of an unconstrained array type.
>>
>> For example, String is an unconstrained array type. If we have
>>
>> function F (S : in String) return Natural;
>>
>> V : String (1 .. 10);
>> C : Natural;
>>
>> then it's perfectly legal to call F with V as its actual parameter:
>>
>> C := F (S);
>>
>>> Also, and the main point of my post, I've found that I can place the
>>> unconstrained array inside a record with a distriminant and this seems
>>> to solve all our problems. We don't have to use array initialisers and
>>> we can get pointers to aliased objects that can be easily passed to
>>> the math functions.
>> Here is your problem. There should be no reason to pass explicit pointers to
>> these functions. Your best solution is to rewrite or change your library.
>>
>> --
>> Jeff Carter
>> "Drown in a vat of whiskey. Death, where is thy sting?"
>> Never Give a Sucker an Even Break
>> 106
> 
> As we have very large array's we're using something like:
> 
> 
> type Unconstrained_Array is array ( Integer range <> ) of Integer;
> type Unconstrained_Array_Pointer is access all Unconstrained_Array;
> 
> procedure F (S : in Unconstrained_Array_Pointer);
> 
> V : Unconstrained_Array := (1 .. 10_000 => 0);
> V_Ptr : Unconstrained_Array_Ptr :=
> Unconstrained_Array'unchecked_Access
> 
> F (V_Ptr);
> 
> 
> Note the use of the array intialiaser, if this isn't used then the
> pointer is no longer compatible.
> 

I think the problem here is you are assuming you need to pass a pointer 
to the function in order to avoid a copy. This is an incorrect assumption.
Just make the function take in the unconstrained array. No large copy 
will be made.