[Feature, patch] Introduce the AS/IS operator for arbitrary enumeration types

Original Reporter info from Mantis: kluug.net @onpok

• Reporter name: Ondrej Pokorny

Description:

The following patch introduces the AS/IS operator for arbitrary enumeration types - a new built-in conversion from integer to enum with range check.

A test unit for FPC test suite is included as well.

Steps to reproduce:

type
  TMyEnum = (zero, one, two);
var
  E: TMyEnum;
begin
  E := 1 as TMyEnum; // OK
  E := -1 as TMyEnum; // error 219
end;

Additional information:

As discussed in fpc-mailing list:

http://lists.freepascal.org/pipermail/fpc-devel/2017-July/038029.html
http://lists.freepascal.org/pipermail/fpc-devel/2017-July/038030.html

Mantis conversion info:

• Mantis ID: 33603
• Version: 3.1.1
• Monitored by: » @martok (Martok), » Vincent (Vincent Snijders), » Akira1364 (Akira1364), » @CuriousKit (J. Gareth Moreton)