On Jan 4, 2012, at 8:39 AM, Mark S. Miller wrote:
> ...
>
> Here's an interesting compromise I consider perfectly reasonable. We don't
> *mandate* any ES6 code features be available in ES6 non-strict mode. But we
> don't prohibit them either. For any ES6 features that have no dependence on
> mode, like destructuring, we mandate that they be present in strict code, and
> we make them normative optional (the new Appendix B category) in non-strict
> code. Implementors are free to implement them or not in non-strict mode, but
> if they implement them, it must mean the same thing as the mandated meaning
> in strict code.
I don't think we every contemplated forbidding implementations from extending
non-strict modes with versions of new features ES6 features.
However, your assumptions that destructuring has has no mode dependencies is
wrong and a good example of why it is not so trivial to "include" it in
non-strict code. Here are some of the dependencies I've already run into WRT
formal parameter destructuring:
using 'arguments' (or 'eval') in a formal parameter destructuring
pattern or as a rest parameter - currently forbidden by strict mode
effect of multiple use of the same name - currently forbidden in strict
mode but currently allowed in non-strict mode
interaction between new formal parameter forms and non-strict mode
arguments object
how is declaration instantiation order for non-strict functions impacted
by parameter default value expressions
can the temporal dead-zone rules related to parameter default value
expression evaluation in strict mode also apply to non-strict functions
These tend to be subtle issues and the "right" answer is not always obvious.
If different implementors decided to add the new formal parameter affordances
to non-strict mode, without any guidance, they would likely come up with
differing solutions to some of these issues and hence create imcompatabilities.
BTW, The simplest way to work around these issues, that I've found, would be
to say that any function that uses any new formal parameter syntax is
implicitly a strict mode function.
Allen
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