[GROOVY-7123] In traits field assignment is not an expression

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.3.7
• Fix Version/s: 2.3.8, 2.4.0-beta-4
• Labels: traits
• Assignee: Cédric Champeau
• Reporter: Dinko Srkoc
• Created: 19/Oct/14 18:27
• Updated: 15/Oct/15 18:15
• Resolved: 05/Nov/14 03:50

Description

Assigning a value to a field in a trait doesn't produce a value as a result:

trait A {
    def foo
    def bar() { foo = 42 }
}
class C implements A {}

assert new C().bar() == null // should be 42

Groovy treats assignments as expressions, returning the value from the RHS, but traits break that semantics.

Using the AST Browser it can be seen that bar() calls A$Trait$Helper.bar(this), which in turn calls $self.A_foo$set(42) which returns void ($self is an instance of C) - hence null that bar() returns.