Change in behavior of & operator between 83 and 9x?

Change in behavior of & operator between 83 and 9x?

[Paul Graham]

If an array type A has component type B which is itself an array type, is it
possible to concatenate two arrays of type B to produce an array of type A?
For instance:

    package foo is
	type my_string is array(1 .. 3) of character;
	type my_string_vector is array(positive range <>) of my_string;
	c1 : my_string_vector := "abc" & "def";
    end;

In this example, I want the value of the concanenation to be equivalent to

	("abc", "def")	-- my_string_vector(1 to 2)

But it can also be interpreted as

	"abcdef"	-- string(1 to 6), my_string(1 to 6), ???

which does not match the type of c1.  

The 83 RM (4.5.3(4)) states "if both operands are one-dimensional arrays,
the result of the concatenation is a one-dimensional array whose length is
the sum of the lengths of the operands ...".  Clearly the concatenation of
two strings is always a string, and never an array of strings.

But the 9x RM defines the result of a concatenation in terms of its result
type.  In the above example the result type is known to be my_string_vector.
Thus the "&" should be "&"(x, y : my_string) return my_string_vector.

Is my understanding wrong, or is this an incompatibility between the 83 and
9x versions of Ada?

Paul
--
Paul Graham 	graham@compass-da.com	Compass Design Automation, Inc.
(speaking only for myself)	"Cekoslovakyalilastiramadiklarimizdanmissiniz."

Re: Change in behavior of & operator between 83 and 9x?

[Keith Thompson @pulsar]

In <19941006.090935.490@vnet.ibm.com> karthurs@vnet.ibm.com (Keith Arthurs) writes:
> In article <GRAHAM.94Oct5120449@canopus.clsi.COM>,
>  on 05 Oct 1994 16:04:49 GMT,
>  Paul Graham <graham@clsi.COM> writes:
> >
> >If an array type A has component type B which is itself an array type, is it
> >possible to concatenate two arrays of type B to produce an array of type A?
> >For instance:
> >
> >    package foo is
> >     type my_string is array(1 .. 3) of character;
> >     type my_string_vector is array(positive range <>) of my_string;
> >     c1 : my_string_vector := "abc" & "def";
> 
> In Ada 83 'my_string_vector' would need to be constrained (1 .. 2)
> (lrm 3.6.1:6)
> 
> >    end;
> >
> >In this example, I want the value of the concanenation to be equivalent to
> >
> >     ("abc", "def")  -- my_string_vector(1 to 2)
> 
> This is a correct interpretation of 'my_string_vector', it is a two
> dimensional array

A quibble: it's not a two dimensional array, it's a one dimensional array
whose component type is also a one dimensional array.  (Unlike Pascal,
for example, Ada does distinguish between these two cases.)

For example:

    type Array_1d    is array(1 .. 3) of Integer;
    type Array_1d_1d is array(1 .. 3) of Array_1d;
    --
    -- Array_1d_1d is a 1-d array of 1-d arrays
    --

    type Array_2d    is array(1 .. 3, 1 .. 3) of Integer;
    --
    -- Array_2d is a 2-d array
    --

Just to add to the confusion, both types use the same syntax for aggregates:

    Obj_1d_1d: Array_1d_1d
        := (1 => (1, 2, 3),
            2 => (4, 5, 6),
            3 => (7, 8, 9));

    Obj_2d: Array_2d
        := (1 => (1, 2, 3),
            2 => (4, 5, 6),
            3 => (7, 8, 9));

-- 
Keith Thompson (The_Other_Keith)  kst@alsys.com
TeleSoft^H^H^H^H^H^H^H^H Alsys, Inc.
10251 Vista Sorrento Parkway, Suite 300, San Diego, CA, USA, 92121-2718
/user/kst/.signature: I/O error (core dumped)