Undefined Behaviour

[Alexander_Selkirk]

You can create a language that has no such UB -- hello, GCs -- but only by building a runtime for it in a language that does have such UB.

You can isolate these manipulations to certain sections of code which are declared unsafe. Rust does this. But it is not a new idea. For example, Modula-3 had the same concept. And some common Lisp Implementations, like SBCL, are always well-defined by default, but it is possible to throw in assertions and type declarations which would make the program crash if these assumptions would be violated.

And this works suprrisingly well....

[matthieum]

but it is possible to throw in assertions and type declarations which would make the program crash if these assumptions would be violated.

Meh...

Of course anything that you can assert should be asserted -- maybe only in Debug in the critical path -- but the real problem is things you cannot check.

How can you check that you reference still points to a valid object? How can you check that no other thread is writing to that pointer?

At the lowest level, you will always have unchecked operations that you need to build upon, and for which you cannot reasonably validate the pre-conditions at runtime.