# Ada Programming/Attributes/'Range

## DescriptionEdit

The meaning of the attribute depends on the meaning of the prefix X.

If X is a scalar subtype, X'Range represents the range of valid values for that subtype, i.e. it is the same as the subtype itself.

If X is a constrained array subtype or an array object, X'Range denotes the index range of X.

In any case, X'Range is equivalent to X'First .. X'Last, but X is only evaluated once.

If X is multidimensional, the attribute needs a *static* parameter N to identify the N-th index; 'Range (1) is the same as 'Range.

X'Range (N) is equivalent to X'First(N) .. X'Last(N), but X is only evaluated once.

## ExamplesEdit

type T is range 1..10; -- T'Range is equal to T

type A is array (T) of S; -- these three A'Range is the same as T type A is array (T'Range) of S; -- declarations type A is array (T'First .. T'Last) of S; -- are equivalent type B is array (T range <>) of S; -- B'Range is illegal (B is unconstrained) subtype SB is B (2 .. 5); -- SB'Range is the same as 2 .. 5 type M is array (Boolean, T) of S; -- M'Range is equivalent to M'Range (1), which is Boolean—M'Range (2) is the same as T OA: A; -- OA'Range is the same as T OB: B (2 .. 5); -- OB'Range is equal to 2 .. 5