[GROOVY-7427] TupleConstructor should allow a mechanism to switch off automatic parameter defaults

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 2.5.0-alpha-1
• Component/s: xforms
• Assignee: Paul King
• Reporter: Paul King
• Created: 18/May/15 07:33
• Updated: 02/May/17 02:03
• Resolved: 18/May/15 12:45

Description

When using @TupleConstructor, it automatically provides defaults for the parameters. This is particularly useful behavior since it allows parameters which can remain as their default (user provided or null/0/false) can be left out of the constructor. In particular, a no-arg constructor corresponds to the case of all arguments left out. This is exactly the kind of constructor which Groovy needs for default named-argument processing.

Having said that, there are times when all is required is a single simple constructor having all of the classes properties. This issue allows a parameter defaults=false to be set to enable this new behavior.

For this class:

@TupleConstructor
class Person {
    String first, last
    int age
}

The following normal constructor is produced:

Person(String first=null, String last=null, int age=0) { this.first = first //etc... }

After Groovy's compilation phases are complete, the following constructors are visible to Java:

Person(String first, String last, int age) { //... }
Person(String first, String last) { this(first, last, 0) }
Person(String first) { this(first, null) }
Person() { this(null) }

Adding defaults=false as a parameter to TupleConstructor means that just the first of these will be produced. If any of the properties has a default value, when this setting is made false, an error will be flagged.