Use "default" keyword for default visibility.

[Adrian Kuhn]

PROJECT COIN SMALL LANGUAGE CHANGE PROPOSAL FORM v1.0

AUTHOR(S): Adrian Kuhn

OVERVIEW

Allow the "default" keyword to be used as modifier for default  
visibility. In strict mode, missing use of default is a warning /  
error, in compatibility mode both the current (ie no default keyword)  
and the new syntax are accepted.

FEATURE SUMMARY: Use "default" keyword for default visibility.

MAJOR ADVANTAGE: The missing keyword for default visibility breaks the  
symmetry of visibility modifiers. Since it is the only implicit  
modifier, omitting any of the three explicit modifiers by mistake may  
be the source of unexpected behavior and thus hard to track down bugs.  
(There was an example on a blog post recently, but I cannot find it  
know).

MAJOR BENEFIT: Symmetry of visibility modifiers is restored.

MAJOR DISADVANTAGE: Two ways to express the same thing (in  
compatibility mode).

ALTERNATIVES: Using a comment such as /* default */ is not an  
alternative since such comments are not processed by the compiler.

EXAMPLES

public class C {
	default Field f;
}

SIMPLE EXAMPLE: See above.

ADVANCED EXAMPLE: None.

DETAILS

SPECIFICATION: "default" is already a keyword and introducing it as a  
new visibility modifier is save, it does not lead to ambiguous grammar.

COMPILATION: Same as now for implicit default visibility.

TESTING: Same as now for implicit default visibility.

LIBRARY SUPPORT: None.

REFLECTIVE APIS: None.

OTHER CHANGES: None.

MIGRATION: Compatibility mode allows both, implicit and explicit  
default visibility, to be used at  the same time.

COMPATIBILITY

BREAKING CHANGES: None.

EXISTING PROGRAMS: Work fine in compatibility mode.

REFERENCES

EXISTING BUGS: To my best knowledge, none.

URL FOR PROTOTYPE (optional):