for-loops and declaration-like init expressions

[Andreas Rossberg]

On 5 June 2014 18:50, Allen Wirfs-Brock <allen at wirfs-brock.com> wrote:
> Over and beyond the breaking change WRT function, I really don’t see the value in such a restriction.  There are many pointless or nonsensial things that can be written as expressions.  In general, we  don’t complicate the language to make such things illegal.

The point is not so much that it is pointless or nonsensical, but that
it has surprising and arguably inconsistent meaning.

/Andreas


> On Jun 5, 2014, at 7:58 AM, Andreas Rossberg <rossberg at google.com> wrote:
>
>> C-style for-loops allow declarations as init statements, but only some
>> of them. Yet, the others (function and class) are actually
>> syntactically legal in that position as well, because they are simply
>> parsed as expressions. Consider:
>>
>>  let x = 0
>>  for (let x = 1; ;) x  // 1
>>  for (const x = 1; ;) x  // 1
>>  for (function x(){}; ;) x  // 0
>>  for (class x(){}; ;) x  // 0
>>
>> I think these latter two examples violate the principle of least
>> surprise. I wonder if it wouldn't be cleaner to rule them out, by
>> imposing the same lookahead restrictions on for-loop init expressions
>> as there are for expression statements.
>>
>> The one caveat is that for function, that would actually be a breaking
>> change, but is it likely to be a real world one?
>>
>> What do you think?
>>
>> /Andreas
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