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Build Identifier: A popular new language feature in a number of languages (Scala, Cylon) is a concise syntax for immutable object construction. The use case is _not_ intended to support injection of collaborators-- that is still best served by DI. This is intended to provide sugar for the common idiom of passing values into a constructor which need to be assigned to a final field (exposed through a property). So all the time we see java like: public class MyDataValue { private final String x; private final String y; public MyDataValue(String x, String y) { this.x = x; this.y = y; } public String getX() { return this.x; } public String getY() { return this.y; } } Here is the Scala equivalent of that class: class MyDataValue(val x:String, val y:String) You can also have mixed mutability and do: class MyDataValue2(var x:String, val y:String) so x will have get/set property access and y will only have get and will be final. This is a common idiom with tremendous amount of noise reduction. So it might fit well into Xtend. If not, then fair enough. Just thought I would log it for consideration since I didn't see it. Reproducible: Always
An addition that could be done to this to make it even more useful would be to generate withX(String x) and withY(String y) methods which return a "clone" of the instance with the X (resp. Y) property updated according to the argument given to the withX() method. For example val a = new MyDataValue("0", "1") val ax = a.withX("00") val ay = a.withY("11") println(a) println(ax) println(ay) would result in MyDataValue{"0","1"} MyDataValue{"00","1"} MyDataValue{"0","11"} (Obviously with a suitable toString() method... which could also be generated quite easily for these types of classes :)).
This would be an excellent use case for bug #373184
just like @Property we decided to do this now based on an annotation and back-port it to a more generic annotation processing hook, when it's available. Here's the proposal: @Data class Person { String name String firstName val gender = Gender::MALE } 1) all field are treated and marked as final. The internal field's name is renamed to _fieldName. 2) a constructor for the non-initialized fields is generated, the ordering of the parameters is the same as the declaration of the fields. Collections are copied to immutable variants in the constructor. 3) a getter method for each field is generated, if not existing. 4) equals and hash code are generated 5) toString() is generated returning a multiline string in the following form DataClassName { field1 = toStringOfField1 field2 = ... } Constraints: 1) A data class can only refer to immutable data types. That is other data classes and a predefined list of classes. 2) A data class can only extend other data classes. 3) A data class must have the @Data annotation. 4) A data class must have final fields only. 5) A data class must have one constructor. Comments? Anything I missed?
pushed to master
Requested via bug 522520. -M.
