When True is not

Pop quiz! How can the following program …

Writeln(True);
Magic;
Writeln(True);

… output this:?

TRUE
FALSE

Simple!

For..to..step in Delphi!

Today I was porting some legacy code and noticed a weird warning:

Weird warning, I thought. Obviously the loop variable can be passed as a var parameter as the code compiles. Why a warning and not an error, then?

Implementing Record Assignment Operator [2]

Yesterday I hinted at having a working (and easy to use) solution which allows you to detect a record assignment (or copying, if you want) and to access both records (left and right part of the assignment operation). You can also modify record data when an assignment is detected. I also mentioned that my approach is very ugly, unstable, likely to cause problems in future Delphis and so on. You should read this article for the technical details, not to really use my code in an application. You have been warned!

Before I jump to hardcode Delphi stuff, I’d like to mention few different approaches that various smart people have already implemented. Most of them slipped below my radar in the past – and I’m guessing this may be the case for you too – so I’m listing them here in case you want to do more research on the topic.

Implementing Record Assignment Operator [1]

Following the yesterday’s hunch, I did some research and I came up with a way to detect when a record is copied (simple, supported, working everywhere) and even to access both records (source and target) during that operation (unsafe, unsupported and currently working only for Win32).

Now I can write such code: