[GROOVY-10394] SC: operands evaluated multiple times for <=> operator on reference types

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.0-rc-2
• Component/s: Static compilation
• Assignee: Eric Milles
• Reporter: Eric Milles
• Created: 28/Nov/21 15:45
• Updated: 03/Feb/22 22:29
• Resolved: 28/Nov/21 17:22

Description

Similar to GROOVY-7473, consider the following:

@groovy.transform.CompileStatic
class C {
  int i = 0, j = 1
  Integer getA() { i++ }
  Integer getB() { j++ }
  void test() {
    assert (a <=> b) == -1
    print i
    print j
  }
}
new C().test()

In cases where "a" and "b" are not identical and non-null, each is evaluated 3 times (script prints "34" not "12"). This is not good if "a" and "b" are expensive to compute or have side effects.

BinaryExpressionTransformer converts a <=> b into a === b ? 0 : (a == null ? -1 : (b == null ? 1 : a.compareTo(b)))