Namespaces

Namespaces in FPC

This page contains proposals and ideas, which could lead to the a better implementation of namespaces that what Delphi currently has.

Why?

Namespaces are not perfect, but they do work, and they do greatly reduce the chances for unitname or classname conflicts. Other languages and frameworks (Java, .NET, C++ etc) have already seen the problem and introduced namespace support.

How visible is the unit name conflict problem? Just think, how many projects are there that use the unit names (or would like to use these common names):

 constants.pas
 utils.pas
 etc...

Extremely common names, and are really good names for what they contain (they describe the purpose of the unit clearly), so why can't we use them in our projects? Namespaces will resolve such problem.

• To reduce the chances of conflicting unit names
• Allow developers to use ideal names for units without the worry of conflicting unit names with the FPC compiler or other component libraries. eg: constants.pas or utils.pas or strutils.pas
• No need for cryptic 2 or 3 letter prefixes to unit names.

Interested Parties

• Graeme Geldenhuys

Usage Examples

Please add any new ideas to the end of the list.

Suggestion 1 - "dotted unit name notation"

Use the same style as implemented in Delphi 2009 onwards.

Pros

• Delphi compatible

Cons

• The force rather long unit names. eg: freepascal.rtl.classes.pas
• Unit names now contain a '.' character which doesn't make them truly valid identifiers.
• Ambiguities could appear, but they are rather easy to overcome with a simple language rule. Object Pascal already have many language rules, this will just be a new one. See the following Mantis report for details: Mantis report 14439

Suggestion 2 - new keyword & new compiler parameter

This idea works similar to Compiler Defines. They can be applied to a unit, or to a project as a whole. Add a new keyword namespace <value> to the Object Pascal language that gets added to the unit line of a source file. Also add a new -namespace=<value> compiler parameter to apply a namespace to a whole project

Pros

• Namespaces can be applied per unit or for a whole project. The unit specific namespace takes preference.

 unit buttons namespace fpgui;
 uses
   Classes
  ...
 end.

• Namespaces can be applied via the compiler command line parameter so no need to modify each individual unit.

 fpc -namespace=fpgui buttons.pas groupbox.pas panel.pas

• Least amount of intrusion to existing code.
• Unit names still stay short
• Unit names are still valid identifiers (unlike the "dotted" notation of Delphi).

Cons

• ?

Suggestion 3 - directory layout

Pros

• ?

Cons

• Similar to what JAVA does, though I see lots of issues with this idea because FPC supports multiple search and library paths per project.