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Exceptions.md

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Virgil Exceptions

Virgil III does not have an exception handling mechanism. If your program causes a violation of the safety checks, it is immediately terminated and a stacktrace is printed which includes accurate source information. This is in preference to segmentation faults or silent memory corruption in languages like C, but more draconian than languages like Java.

The exception types

Your program has the unique opportunity to generate the following errors at runtime:

  • !NullCheckException - upon access to a null object, array, or function
  • !TypeCheckException - upon a failed cast
  • !BoundsCheckException - upon an out-of-bounds array access
  • !LengthCheckException - when attempting to create an array with negative length
  • !UnimplementedException - when attempting to call an abstract method
  • !DivideByZeroException - upon a division or modulus with 0 divisor
  • !HeapOverflow - if there is insufficient space in the heap
  • !StackOverflow - if there is insufficient space to hold the stack

The exclamation points are to get your attention! You can avoid these errors by not doing that.

Future Compatibility

Virgil may have an exception-handling mechanism in the future. The implications of adding a fully-general exception handling mechanism have not been fully considered. Experience with other language's exception handling mechanisms is that they are extremely tricky to get right, add a lot of complexity to the runtime system and compiled binaries, and can lead to terrible application APIs.

Your programs will be punished severely for their failings.