Quick start manual

Data types, variables, and constants 5-9
Simple types
You can use numeric constants and characters (string constants of length 1) to define
subrange types:
type
SomeNumbers = -128..127;
Caps = 'A'..'Z';
When you use numeric or character constants to define a subrange, the base type is
the smallest integer or character type that contains the specified range.
The LowerBound..UpperBound construction itself functions as a type name, so you can
use it directly in variable declarations. For example,
var SomeNum: 1..500;
declares an integer variable whose value can be anywhere in the range from 1 to 500.
The ordinality of each value in a subrange is preserved from the base type. (In the
first example, if Color is a variable that holds the value Green, Ord(Color) returns 2
regardless of whether Color is of type TColors or TMyColors.) Values do not wrap
around the beginning or end of a subrange, even if the base is an integer or character
type; incrementing or decrementing past the boundary of a subrange simply converts
the value to the base type. Hence, while
type Percentile = 0..99;
var I: Percentile;
ƒ
I := 100;
produces an error,
ƒ
I := 99;
Inc(I);
assigns the value 100 to I (unless compiler range-checking is enabled).
The use of constant expressions in subrange definitions introduces a syntactic
difficulty. In any type declaration, when the first meaningful character after = is a left
parenthesis, the compiler assumes that an enumerated type is being defined. Hence
the code
const
X = 50;
Y = 10;
type
Scale = (X - Y) * 2..(X + Y) * 2;
produces an error. Work around this problem by rewriting the type declaration to
avoid the leading parenthesis:
type
Scale = 2 * (X - Y)..(X + Y) * 2;