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Delphi: types you cannot deprecate

Posted by jpluimers on 2021/05/06

Deprecating all types in a unit besides deprecating the unit itself will cause a hint and warning storm. Especially in projects having a lot of hints and warnings (taking over maintenance of a legacy project comes to mind) this can be very helpful to spot these locations inside many files where some obscure unmaintained unit like GIFImage.pas is still used.

[WayBack] TGIFImage for Delphi | MelanderBlog got donated to (then CodeGear, now Embarcadero) for inclusion in Delphi 2007. It was, as GifImg unit, but only documented since the [WayBack] Delphi 2009 GIFImg Namespace). For more information: delphi 2007 gifimg unit – Google Search

Delphi allows you to deprecate a lot of types, but you cannot deprecate these forms:

  • array [...] of TSomeType
  • ^TSomeType
  • class of TSomeType
  • procedure(...) ...
  • function(...): TSomeType ...
  • reference to procedure(...) ...
  • reference to function(...): TSomeType ...

Putting a deprecated 'use SomeUnit.TSomeOtherType' will fail with:

  • either a compiler error  pair
    • E2029 ';' expected but identifier 'deprecated' found“.
    • E2029 '=' expected but string constant found
  • a compiler error
    • E1030 Invalid compiler directive: 'DEPRECATED'

You can enumerate these kinds of types:

  • enumerations
  • records
  • classes, but only a full class declaration, so
    • not the class forward declaration like TMyClass = class
    • not a shortened class declaration like TMyException = class(Exception), this has to be the full TMyException = class(Exception) end deprecated 'reason';
  • methods only after the last separating ; of the method (so the virtual form is like procedure Name(...); virtual; deprecated 'use another method';)
  • named constants
  • global variables

The last few are not technically types, but included for completeness.

–jeroen

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