Description Matt Heitz 2011-08-24 12:27:54 EDT

This work needs to be completed in Iteration 13.  Prioritize it ahead of other enhancements, even if they'll have to be pushed out of the iteration.

[The following is the section on Nullability from http://wiki.eclipse.org/EDT:EGL_Language_Statements.]

Variable declarations, function parameters, and function return types may end with a question mark to indicate that they're nullable. Nullability means that a variable may really be null. It's not an "I'm null" flag like in RBD.  Even reference variables can be nullable.

A NullValueException will be thrown if you try to access a field or function of a null variable, even a record. A NullValueException will be thrown if a null variable is an operand to a math operator, an array access, a substring access, a comparison, or a bitwise operator. The string concatenation operators will work the same as in RBD with respect to nulls. :: treats null as the empty string, and ?: results in null if either operand is null. A question mark won't be allowed on the second operand of the AS and ISA operators (the name of the type).

A validation check will ensure that things which can't be instantiated (interfaces, and types with private default constructors) must be declared nullable. Constructors can be defined in ExternalTypes and handlers.

You can't assign null to something that's not nullable.  We'll give a validation error on notNullableVariable = null; and a runtime error on notNullableVariable = nullableVariable; when the nullableVariable is null.