Hi,
Recently I learned that you can have writeable typed constants. That
sounds rather like an oxymoron to my. Writeable constants make no sense,
is that then simply a variable? What is the use of a writeable typed
constant?
Below is two examples of how they can be used, and support for them are
toggled with the compiler directive $J.
In both these cases I would think a variable would make a lot more
sense. For the Singleton implementation, you simply need to specify a
unit wide AppSingleton variable in the implementation section (so that
it's not completely global or visible to other units.
Can anybody explain the point of writeable typed constants?
const
foo: Integer = 12;
begin
foo := 14;
end.
===============================
// Singleton implementation using typed constants
function gAppManager: TApplicationManager;
const
{$IFDEF DELPHI}{$J+}{$ENDIF}
AppSingleton: TApplicationManager = nil;
{$IFDEF DELPHI}{$J-}{$ENDIF}
begin
if not Assigned(AppSingleton) then
AppSingleton := TApplicationManager.Create;
Result := AppSingleton;
end;
Regards,
- Graeme -
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