With the introduction of Delphi 2009, a lot of features are added to the Object Pascal language. Almost anybody knows about generics and closures, but there are more, and not all of them are documented (or at least hard to find).
What are the lesser known language constructs of OP that you know about?
Exit
Within functions, Exit can have a parameter:
function IsMagic(const AValue: Integer): Boolean;
begin
if AValue<0 then Exit(False);
...
end;
Deprecated
The deprecated hinting directive can have an optional message:
const
cDeviceCRT = 12 deprecated 'Why not use a flatscreen';
The message is shown with the deprecated warning. And it must be a string literal and no const expression. The other hinting directives (platform, library, experimental) are excluded.
{$pointermath ON} to do pointer arithmetic.
This can be used in either of two ways:
Types or aliases defined while {$POINTERMATH ON} is in effect will have C-like pointer semantics;
Expressions parsed while {$POINTERMATH ON} is in effect may use pointers in a C-like fashion.
By C-like, we mean:
Old-style "object" types still exist, and even support inheritance, visibility modifiers and virtual/overrides.
Here an example :
type BaseType = object
protected
FValue: Integer;
public
procedure Initialize(const aValue: Integer); virtual;
end;
type ExtensionType = object(BaseType)
private
FExtra: Integer;
public
procedure Initialize(const aValue: Integer); override;
end;
You do need to be aware of a few facts about this :
That being said, I do think it's an nice alternative to records (which don't support inheritance), and classes (which aren't stack-managed).
The fact that WinAPI wrappers have changed from -A (Ansi) to -W (Wide) implementations. Together with the change of String to UnicodeString and Char to WideChar, this has been an almost completely transparent change for a lot of code using these. The benefit is: no more hidden internal translations to Ansi, improving speed and compatibility.
Don't forget about {$SCOPEDENUMS ON}: enumerations defined while this is in effect will not have their values added to the unit / program scope directly, but will have to be explicitly qualified with the enumeration name, just like in C#.
FWIW, (almost) all enumeration values can be explicitly qualified by enumeration name (the main exception I'm aware of is Boolean), like this:
type
TMyBool = (T, F);
begin
Writeln(Ord(TMyBool.T));
end.
TextHint support for edits and combo boxes in XP and later. Windows TextHint support for combo boxes was officially introduced in Vista. Delphi is doing some trickery behind the scenes on XP.
I've been using Delphi since version 3 and only just today discovered threadvar
It lets you do Thread Local Storage by using some compiler magic
Will probably never use it mind you!
Another nice one. Use the constructor constraint with generics:
type
TMyClass<T: TMyOtherClass, constructor> = class
public
function NewOther: T;
end;
function TMyClass.NewOther: T;
begin
Result := T.Create;
end;
This is not possible without the constructor constraint.
If you have D2009 then you can probably download the free PDF of Marco Cantu 'Delphi 2009 Handbook'. It's on the Codegear site for registered users, but I bought a copy as well. He lifts the lid on loads of low-level D2009 stuff. You can read more about it here