Optional assignment operator

[Isiah Meadows]

You could file an issue there, where it's more likely to get seen by
interested parties. The basic concept is basically reversed augmented
assignment, where `a @= b` usually means `a = a @ b`, you'd want
something like `a =@ b` meaning `a = b @ a`. (Operator is up for
debate, and `=-` conflicts with negation.)

I could see the use of it - `??` is the most common case for me, but a
reverse subtraction or easy reciprocal division would also be
convenient in some cases. I'm neutral on the idea, though.

-----

Isiah Meadows
me at isiahmeadows.com
www.isiahmeadows.com


On Thu, Jul 5, 2018 at 4:53 PM, Jacob Pratt <jhprattdev at gmail.com> wrote:
> This idea isn't quite the same as ||=, as that includes any falsey value,
> nor ??=, as that includes null. My thought was to be able to set a property
> if there is a value that exists (which would include null, but not
> undefined).
>
> It's certainly similar — should this be considered for addition to that
> existing proposal?
>
> My thinking was along the lines of "Set this if there is something to set.
> If not, just keep going". It can be done with an if statement, but would
> require a temporary reference due to getters and/or method calls.
>
> jhpratt
>
> On Thu, Jul 5, 2018 at 3:08 AM, Isiah Meadows <isiahmeadows at gmail.com>
> wrote:
>>
>> How about you all take a look here:
>> https://github.com/tc39/proposal-logical-assignment
>>
>> Originally, it was at
>> <https://github.com/tc39/proposal-nullish-coalescing>, but here
>> <https://github.com/tc39/proposal-nullish-coalescing/issues/1>, it was
>> discussed and pushed off to the logical assignment proposal as it was
>> also a short-circuiting operator, even though it wasn't really a
>> *boolean* operator.
>>
>> -----
>>
>> Isiah Meadows
>> me at isiahmeadows.com
>> www.isiahmeadows.com
>>
>>
>> On Wed, Jul 4, 2018 at 10:25 PM, Sam Ruby <rubys at intertwingly.net> wrote:
>> > On Wed, Jul 4, 2018 at 7:12 PM, Jacob Pratt <jhprattdev at gmail.com>
>> > wrote:
>> >> I've been having this thought recently, after running across a
>> >> potential use
>> >> case in practice. There will likely be conditional accessors at some
>> >> point
>> >> in the future (with optional chaining), but there will not be
>> >> conditional
>> >> assignment.
>> >>
>> >> My thought was to have the following:
>> >>     this.foo ?= params?.foo;
>> >> which can be desugared to
>> >>     if (($ref = params?.foo) !== undefined) { this.foo = $ref; }
>> >>
>> >> I would strictly check for undefined, rather than nullish, as anything
>> >> other
>> >> than undefined would indicate that a value is present that can be set.
>> >> If no
>> >> value is present (such as a missing key on an object), nothing would be
>> >> set.
>> >> A reference must be used for the general case, as the object being
>> >> assigned
>> >> (the RHS) could be a function or getter with side-effects.
>> >>
>> >> Not sure if it should be ?= or =?, as it would look somewhat odd (IMO)
>> >> for
>> >> things like ?+= or +=?.
>> >>
>> >> Initial thoughts?
>> >
>> > Perl and Ruby have "||=" and "&&=" operators.  They don't strictly
>> > check for undefined in either language.
>> >
>> > These operators are frequently used (in particular, "||=").  I do miss
>> > them.
>> >
>> > Looking at the node.js source:
>> >
>> > $ find . -name '*.js' -type f | xargs egrep ' (\S+) = \1 \|\| ' | wc -l
>> >    1416
>> >
>> > $ find . -name '*.js' -type f | xargs egrep ' if \(!(\S+)\) \1 = ' | wc
>> > -l
>> >      497
>> >
>> > Nearly 2K occurrences in one code base.
>> >
>> >> Jacob Pratt
>> >
>> > - Sam Ruby
>> > _______________________________________________
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>> > es-discuss at mozilla.org
>> > https://mail.mozilla.org/listinfo/es-discuss
>
>