{"id":1207,"date":"2012-09-20T08:20:46","date_gmt":"2012-09-19T20:20:46","guid":{"rendered":"https:\/\/www.deltics.co.nz\/blog\/?p=1207"},"modified":"2012-09-20T09:59:43","modified_gmt":"2012-09-19T21:59:43","slug":"adventures-in-syntax-something-old-something-new-etc","status":"publish","type":"post","link":"https:\/\/www.deltics.co.nz\/blog\/posts\/1207\/","title":{"rendered":"Adventures in Syntax: Something Old, Something New etc…"},"content":{"rendered":"[Estimated Reading Time: <\/span> 8<\/span> minutes]<\/span><\/span>

As the post title says, this will be a brief detour through some features of the Pascal language and a presentation of some (theoretical) alternatives that could have been introduced instead. That is, some are real but little known syntax, others are what I think might be preferable to the syntax we actually have. <\/p>\n

<\/p>\n

So, as the old saying goes, let’s take them in order: Something Old, Something New, Something Borrowed and Something Blue…<\/p>\n

Something Old<\/h3>\n

Parameterless Implementations for Methods With Parameters<\/em><\/strong><\/p>\n

Did you know that you can omit the parameters on your method implementations?<\/p>\n

\r\nunit Parameterless;\r\n\r\ninterface\r\n\r\n  type\r\n    TFoo = class\r\n      procedure Bar(const aParam: Integer);\r\n    end;\r\n\r\nimplementation\r\n\r\n  procedure TFoo.Bar;\r\n  var\r\n   i: Integer;  \r\n  begin\r\n    i := aParam;  \/\/ << all good, the parameter declaration isn't needed\r\n  end;\r\n\r\nend.\r\n<\/pre>\n
I recently saw this described as a bug that was fixed only as recently as Delphi 2007.<\/p>\n
Well, it was never a bug and in fact it still compiles just fine even in XE2 and most likely XE3 (on the machine that I am writing this I don’t have XE3 so cannot verify).  I first came across this language feature in some Delphi 5 code, coincidentally while investigating an issue that did<\/strong> turn out to be a compiler bug (but entirely unrelated to this language feature).<\/p>\n
Ironically the mis-identification of this as a bug came paired with a complaint that the self-documenting interface\/implementation declarations in Pascal resulted in unnecessary duplication of declarations – something that this particular feature of Pascal is obviously designed to reduce<\/em>.<\/p>\n
One problem that this very old feature of the Pascal language suffers from is that in more modern implementations of the language it is now possible to have multiple versions of the same method, each of course having different parameters.  i.e. overloads<\/strong>.  In that situation the compiler will of course have to insist that you have matching parameter declarations in your implementations, simply so it can match each implementation with the corresponding interface declaration.<\/p>\n
But otherwise, the re-declaration of the parameters in the implementation is optional, by design.  Whose design ?  Well, the original language.<\/p>\n
In effect – and in practice – the interface declaration is a forward declaration<\/em> of the formal parameters for the methods in the class, and ANSI Pascal doesn’t require the formal parameters to be repeated when the forward declaration is completed by an actual implementation.<\/p>\n
\r\n  procedure FooBar(aParam: Integer); forward;\r\n\r\n  procedure FooBar;\r\n  var\r\n      i: Integer;\r\n  begin\r\n    i := aParam * 2;\r\n  end;\r\n<\/pre>\n
The Parameterless<\/strong> unit code (not the code above but the snippet before that) compiles just fine in Lazarus\/FPC with the following syntax settings for the compiler:<\/p>\n