Package org.ek9lang.compiler.phase1

Class ValidPreFlowAndReturnOrError

java.lang.Object
org.ek9lang.compiler.common.RuleSupport
org.ek9lang.compiler.phase1.ValidPreFlowAndReturnOrError
All Implemented Interfaces:
BiConsumer<EK9Parser.PreFlowStatementContext,EK9Parser.ReturningParamContext>
class ValidPreFlowAndReturnOrError extends RuleSupport implements BiConsumer<EK9Parser.PreFlowStatementContext,EK9Parser.ReturningParamContext>
Checks that if a return is used.

(i.e. as parent context is part of an expression), then if a 'preflow' is employed that the 'preflow' is NOT a guard.

The reason for this is to prevent the 'lhs' of an expression resulting in being uninitialized should the 'guard' trigger the prevention of the whole expression on the rhs not being executed. So, for normal statements using while, for, try, switch the guard can be useful and stop lots of checks and wasted processing.

But if this same approach is allowed with the expression form, it means that we have a dangling and uninitialised 'lhs' variable. This is a bigger problem in a 'pure' scope block and we always drive to ensure variables are only assigned to once, except for returns and other very small cases (loop variables etc).