Nullablity

[Graydon Hoare]

Nicolas Cannasse wrote:

> As for values initialization, it should be enforced by the compiler.
> This can easily be done for member and local variables by using some
> recursive flow algorithm.

I know you're coming from the background of compiling large, highly 
structured programs, and I respect that perspective. I personally agree 
with what you've said here, in the context of a language *for my 
programming needs*.

But I've also heard a credible argument during the design process: that 
the majority of JS code on the web is tiny little fragments, one liners, 
often fragments that only run zero or one times, and sometimes running 
on a cell phone. Keeping the "defaults" easy to compile is a priority 
for at least some of the language implementers. This means dataflow 
algorithms are unappealing: local expression-type inference is about all 
we want to pay for. We do not want to reimplement Java's definite 
assignment rules or similar.

We've talked through many alternatives, and I agree that the topic is 
not yet exhausted. Some syntactically distinct form that covers for the 
same task is possible. We've discussed C++-style initializer syntax for 
example, or ML-style construction-from-a-set-of-expressions. I'm sure 
there are other potential options, but we must keep the tradeoffs in mind.

-graydon