Description Konstantin Komissarchik 2011-06-06 22:23:58 EDT

Consider the case where a property holds an enum and you need to check to see if the property holds one of three enum values.

You can write an expression like this one:

${ ShapeType == 'TRIANGLE' || ShapeType == 'RECTANGLE' || ShapeType == 'SQUARE' }

But that's quite verbose, especially as the number of items to check goes higher. There can also be a problem if LHS of the comparison is an expression rather than a simple property access. Using this pattern would re-evaluate the expression multiple times.

We need something equivalent to SQL IN operator. We should be able to write the above expression like so:

${ ShapeType IN List( 'TRIANGLE', 'RECTANGLE', 'SQUARE' ) }

To do this we need two things: (a) List function that can turn an arbitrary number of operands into a list and (b) IN operator.