WhereToPlaceComments

Michalis Kamburelis edited this page Jan 7, 2017 · 12 revisions

Basic rule

If you want to assign some description to your item (where item means either a unit, a class, a field, a method, a variable, a type, a constant, a function or procedure…​ really, just anything), you just place a comment directly before the item’s declaration.

Here’s an example of a complete unit with many items documented:

{ Description of MyUnit. }
unit MyUnit;

interface

type
  { Description of TMyClass. }
  TMyClass = class
  public
    { Description of MyField. }
    MyField: Integer;
    { Description of MyMethod. }
    procedure MyMethod;
  end;

  { Description of TMySimpleType. }
  TMySimpleType = 1..100;

  { Description of TMyEnumType. }
  TMyEnumType = (
    { Description of meFirstValue. }
    meFirstValue,
    { Description of meSecondValue. }
    meSecondValue);

const
  { Description of MyConstant. }
  MyConstant = 4;

var
  { Description of MyVariable. }
  MyVariable: Integer;

{ Description of MyProcedure. }
procedure MyProcedure;

implementation
...
end.

You can simply paste the above example into a file like myunit.pas and run pasdoc like this

pasdoc myunit.pas

and pasdoc will generate the documentation for MyUnit (in the default HTML format). All the "Description of …​" comments are nicely shown in the resulting documentation.

More detailed rules

Comment markers

You can use --marker option if you want PasDoc to recognize only comments designated by some special markers.

Multiple fields/variables in one declaration

The case when you declare multiple fields/variables with the same type in one declaration deserves some detailed explanation. This concerns declarations like this:

type
  TMyRecord = record
    { Comment 1 }
    Field1, Field2: Integer;
  end;

var
  { Comment 2 }
  Variable1, Variable2: Integer;

The rule is as follows: it is assumed that the single comment will apply to all multiple fields in the following declaration. So in the example above, Comment 1 will be understood to document both Field1 and Field2 and Comment 2 will be understood to document both Variable1 and Variable2.

Moreover, if you place a comment in the middle of such multiple-declaration, this comment will apply to all following fields/variables within this declaration. See this example:

type
  TMyRecord = record
    { This comment documents Field1 and Field2 }
    Field1, Field2,
      { This comment documents Field3 and Field4 }
      Field3, Field4: Integer;
  end;

var
  { This comment documents Variable1 }
  Variable1,
    { This comment documents Variable2 }
    Variable2: Integer;

Placing comments after the item

Sometimes it is more convenient to place your documentation comment after the documented item, instead of before. You can freely do so by placing the "<" ("less-than") character as the exactly first character of your comment. This tells PasDoc that the given comment should be assigned to the preceding (not the following, as usual) item declaration.

Example:

unit MyUnit;

{< Here you can place a description of MyUnit.
   This is convenient for people that like to always
   keep the "unit UnitName;" declaration
   as the first line of their *.pas files. }

interface

type
  TMyEnumType = (
    meOne, //< Description of meOne
    meTwo, //< Description of meTwo
    meThree //< Description of meThree
  );

  TMyClass = class
    MyField: Integer; //< Description of MyField
    procedure MyProc; //< Description of MyProc
    property MyProp: Integer read MyField write MyField;
      //< Description of MyProp
  end;

  TMyException = class(Exception); //< Description of TMyException

var
  SomeVariable: Integer; //< Description of SomeVariable
  Var1, Var2: Integer; //< Description of Var1 and Var2

implementation
...
end.

If you use a CommentMarker, the "<" character must be placed right after your chosen marker.

Glueing single-line comments

Subsequent //-style comments are "glued" by PasDoc into one comment. If comment markers are required, every single comment must be marked accordingly(?). A back-comment mark is recognized only in the first comment of a sequence. For example these methods of documenting procedure Foo are equivalent:

{ This is
  description of
  procedure Foo. }
procedure Foo;

// This is
// description of
// procedure Foo.
procedure Foo;

procedure Foo;
//< This is
// description of
// procedure Foo.

Multiple comments on an identifier or declaration

When one or more comments precede an identifier, and possibly another back-comment follows it, PasDoc (currently) ignores any but the last applicable comment, which overwrites any preceding comments.

Declarations inside declarations, of e.g. class or record fields, have their own comments. Once such a declaration block is closed, a following back-comment again applies to the "outer" declaration.

In a declaration with multiple identifiers, a "<" back-comment applies exactly to the preceding identifier. An eventual forward comment is "canceled", i.e. following identifiers in the same declaration will stay uncommented.

type
  // This comment is overwritten later
  TMyEnumType = (
  // Description of meOne
    meOne,
    meTwo, //< Description of meTwo
    meThree
  );
  //< Description of TMyEnumType, *not* of meThree

Common case when comments are not meaningful to PasDoc

As long as we consider only multi-line comments ({ …​ } or (* …​ *)), remember that PasDoc takes into account only the last comment before given item. For example, in the code below, comment Ignored comment is ignored by PasDoc. Description consists only of Description of Foo comment.

{ Ignored comment. }

{ Description of Foo. }
procedure Foo;

In particular, note that when you want to hide some comment (i.e. prevent it from being assigned to the next item) all you have to do is to put an empty (or containing only whitespace) comment right before given item. For example:

{ procedure Foo; }

{ }
procedure Bar;

In the above example, programmer probably temporarily commented out procedure Foo; declaration. To prevent from accidentaly assigning description "procedure Foo;" to procedure Bar, the programmer added "{ }" right before procedure Bar declaration. A "{ }" or "//" has the same effect, but "{ }" is recommended for clarity.

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