# 4.5.3 Binary Adding Operators

#### Static Semantics

The
binary adding operators + (addition) and – (subtraction) are predefined
for every specific numeric type

*T* with their conventional meaning.
They have the following specifications:

**function** "+"(Left, Right : *T*) **return** *T*

**function** "-"(Left, Right : *T*) **return** *T*

The
concatenation operators & are predefined for every nonlimited, one-dimensional
array type

*T* with component type

*C*. They have the following
specifications:

**function** "&"(Left : *T*; Right : *T*) **return** *T*

**function** "&"(Left : *T*; Right : *C*) **return** *T*

**function** "&"(Left : *C*; Right : *T*) **return** *T*

**function** "&"(Left : *C*; Right : *C*) **return** *T*

#### Dynamic Semantics

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:

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;

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.

The upper bound is determined by the lower bound
and the length.

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
is raised if this check fails.

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.

The result of a concatenation
is defined in terms of an assignment to an anonymous object, as for any
function call (see

6.5).

14 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.

#### Examples

*Examples of expressions
involving binary adding operators:*

Z + 0.1 --* Z has to be of a real type *

"A" & "BCD" --* concatenation of two string literals*

'A' & "BCD" --* concatenation of a character literal and a string literal*

'A' & 'A' --* concatenation of two character literals *

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