[fpc-pascal] How can you convert an enum value to string?

[mahris]

I shall talk about FPC 2.6.2.

First of all - there can be enumerations with predefined values.
In 2.6.2, typeinfo for such enumerations does not exist.
So solutions with GetEnumName are limited and cannot be used in general
case.

str(MyEnum,MyString) and writestr(MyString,MyEnum) give correct results also
for enumeraations with assigned values. But there are two problems.
First - definitely function is much more comfortable than procedure.
Second, catastrophical - enumeration variable can contain value out of
definition scope (always contains it, if enumeration does not start from 0).
str in such cases generates runtime error, and program is finished. writestr
generates exception, which can be caught.

So, my current solution - generic class (unfortunately, generic functions
still not implemented in FP). It requires "specialize" statement for every
enumeration we propose to convert.

Definitions:

type
generic Enumstr<T>=class
  class function tostr(value:T):string;
end;

class function Enumstr.tostr(value: T): string;
begin
  try
    writestr(result,value);
  except
    on e:Exception do
      result := '('+IntToStr(integer(value))+')';
  end;
end;

Usage:

type
  TMyEnum = (e1=3, e2=-4, e3);
  TMyEnumStr=specialize Enumstr<TMyEnum>;
var
  MyEnum: TMyEnum;
  MyString: string;
begin
  MyEnum := e2;
  MyString := TMyEnumStr.tostr(MyEnum); // 'e2'
  MyEnum := TMyEnum(25);
  MyString := TMyEnumStr.tostr(MyEnum); // '(25)'




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