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1

{*binary
adding operator*} {*operator
(binary adding)*} {*+
operator*} {*operator
(+)*} {*plus operator*}
{*operator (plus)*} {*-
operator*} {*operator
(-)*} {*minus operator*}
{*operator (minus)*}
The binary adding operators + (addition) and - (subtraction)
are predefined for every specific numeric type *T* with their conventional
meaning. They have the following specifications:

2

3

{*&
operator*} {*operator
(&)*} {*ampersand
operator*} {*operator
(ampersand)*} {*concatenation
operator*} {*operator
(concatenation)*} {*catenation
operator: See concatenation operator*} The
concatenation operators & are predefined for every nonlimited, one-dimensional
array type *T* with component type *C*. They have the following
specifications:

4

5

{*evaluation
(concatenation)* [partial]} For the evaluation
of a concatenation with result type *T*, if both operands are of
type *T*, the result of the concatenation is a one-dimensional array
whose length is the sum of the lengths of its operands, and whose components
comprise the components of the left operand followed by the components
of the right operand. If the left operand is a null array, the result
of the concatenation is the right operand. Otherwise, the lower bound
of the result is determined as follows:

6

- If the ultimate ancestor of the array type was defined by a constrained_array_definition, then the lower bound of the result is that of the index subtype;

6.a

7

- If the ultimate ancestor of the array type was defined by an unconstrained_array_definition, then the lower bound of the result is that of the left operand.

8

[The upper bound is determined by the lower bound
and the length.] {*Index_Check* [partial]}
{*check, language-defined (Index_Check)*}
A check is made that the upper bound of the result
of the concatenation belongs to the range of the index subtype, unless
the result is a null array. {*Constraint_Error (raised
by failure of run-time check)*} Constraint_Error
is raised if this check fails.

9

If either operand is of the component type *C*,
the result of the concatenation is given by the above rules, using in
place of such an operand an array having this operand as its only component
(converted to the component subtype) and having the lower bound of the
index subtype of the array type as its lower bound. {*implicit
subtype conversion (operand of concatenation)* [partial]}

9.a

10

{*assignment operation (during
evaluation of concatenation)*} The result
of a concatenation is defined in terms of an assignment to an anonymous
object, as for any function call (see 6.5).

10.a

NOTES

11

15 As for all predefined
operators on modular types, the binary adding operators + and - on modular
types include a final reduction modulo the modulus if the result is outside
the base range of the type.

11.a

12

13

14

'A' & "BCD"

'A' & 'A'

14.a

{*inconsistencies with Ada
83*} The lower bound of the result of concatenation,
for a type whose first subtype is constrained, is now that of the index
subtype. This is inconsistent with Ada 83, but generally only for Ada
83 programs that raise Constraint_Error. For example, the concatenation
operator in

14.b

X := X(6..10) & X(1..5);

14.c

would raise Constraint_Error
in Ada 83 (because the bounds of the result of the concatenation would
be 6..15, which is outside of 1..10), but would succeed and swap the
halves of X (as expected) in Ada 95.

14.d

{*extensions to Ada 83*}
Concatenation is now useful for array types whose
first subtype is constrained. When the result type of a concatenation
is such an array type, Constraint_Error is avoided by effectively first
sliding the left operand (if nonnull) so that its lower bound is that
of the index subtype.