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groovymetaprogrammingmixins

Mixin empty interface

Is there any way to mixin an empty interface to a groovy object of a wrapped primitive type? What I tried is:

interface B{}
a = new Boolean(false)
b = a.metaClass.mixin(B.class)
assert b instanceof B

The error is "groovy.lang.GroovyRuntimeException: No default constructor for class B! Can't be mixed in."

Solution

  • This isn't a direct answer to your question, but if you're just looking to mark particular Boolean instances, could you use a marker property instead of an interface? For example:

    Boolean.metaClass.marked = false // establish the marker property

mb = new Boolean(false)
mb.marked = true

ub = new Boolean(false)

assert mb.marked
assert ub.marked == false