for-loops and declaration-like init expressions

[Mark S. Miller]

Hi John, for those it is unsurprising that they would be allowed, and that
they would be taken as expressions rather than declarations.


On Thu, Jun 5, 2014 at 8:23 AM, John Lenz <concavelenz at gmail.com> wrote:

> Would this still be legal, in this scheme?
>
>   for ((function x(){}); ;) x  // 0
>   for ((class x(){}); ;) x  // 0
>
>
>
> On Thu, 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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>
>
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-- 
    Cheers,
    --MarkM
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