SpringSource/spring-framework — pull request #172 by aclement (2012-10-23 19:02:21+00:00)
Title: Add SpEL support for increment/decrement operators

With this commit the Spring Expression Language now supports
increment (++) and decrement (--) operators. These can be
used as either prefix or postfix operators. For example:
'somearray[index++]' and 'somearray[--index]' are valid.

In order to support this there are serious changes to the
evaluation process for expressions. The concept of a
value reference for an expression component has been introduced.
Value references can be passed around and at any time the actual
value can be retrieved (via a get) or set (where applicable). This
was needed to avoid double evaluation of expression components.
For example, in evaluating the expression 'somearray[index++]--'
without a value reference SpEL would need to evaluate the
'somearray[index++]' component twice, once to get the value and
then again to determine where to put the new value. If that
component is evaluated twice, index would be double incremented.
A value reference for 'somearray[index++]' avoids this problem.

Many new tests have been introduced into the EvaluationTests
to ensure not only that ++ and -- work but also that the
introduction of value references across the all of SpEL has
not caused regressions.

Issue: SPR-9751