As part of SERVER-59785, we have decided to err on the side of consistency and make $concatArrays not short-circuit in SBE, to match the behavior of the rest of the variadic expressions. However, for expressions that take an arbitrary number of arguments, there is a practical performance benefit to short-circuiting early when it is known that the result should be e.g. null.

This ticket is to consider implementing a uniform policy in SBE, wherein fixed, low-arity expressions always evaluate all arguments, but variadic expressions will attempt to short-circuit when possible for the sake of efficiency.

The list of variadic expressions currently implemented in SBE are

• $concat
• $add
• $multiply