Hi Brendan and Allen, you are both responding only to my point #1. I
consider my point #2 --- cognitive load of the reader on encountering a
rarely seen construct --- to be the more significant criticism here.
On these grounds, your
function f(args: x, y, z) {
is worse. Given how ":" is already used in JS, this suggests that "args" is
either a label name, which the more astute reader can easily disqualify, or
a property name, suggesting some shorthand for named parameters.
Note that I am not saying that the meanings of all syntactic constructs
have to be guessable with no guidance. But the rarely used ones do.
3) Awkward syntax for some rarely used cases is the price of good syntax
for common cases.
On Sun, Nov 10, 2013 at 11:08 AM, Brendan Eich <[email protected]> wrote:
> On the other hand, we are this close in ES6 to relieveing people from
> having to use arguments at all.
>
> I like the intention behind Allen's idea. To defend the concrete syntax a
> bit, one would argue that only the final formal parameter may be prefixed
> with #, and we are free to use # in other ways elsewhere.
>
> If # should be kept reserved even in this context, then perhaps something
> like
>
> function f(args: x, y, z) {
> // use x, y, z freely (they could be patterns)
> switch (args.length) {
> case 1: ...
> case 2: ...
> // etc.
> }
> }
>
> The "label" names a rest parameter for the entire parameter list.
>
> /be
>
>> Mark S. Miller <mailto:[email protected]>
>> November 10, 2013 6:52 PM
>>
>> 1) "#" is one of the few ascii characters we haven't used up yet. Let's
>> not use it up on a minor convenience.
>>
>> 2) Introducing new syntax for use cases that are expected to be frequent,
>> e.g., classes, often pays for its weight. The frequency makes it likely
>> that readers will understand what it is the vast majority of times they
>> encounter it. New syntax that gets used once in a blue moon can only be
>> justified if the pain of doing without in those blue-moon cases is huge. In
>> this case, it isn't. For those rare occasions when they see it, readers are
>> much more likely to guess what "arguments.length" mean that this funny
>> newfangled "#" thing.
>>
>> Code is read much more often than it is written -- at least code that
>> matters. Brevity is useful as a metric only to the degree that it serves as
>> a proxy for cognitive load on the reader.
>>
>>
>>
>>
>>
>>
>> --
>> Cheers,
>> --MarkM
>>
>> _______________________________________________
>> es-discuss mailing list
>> [email protected]
>> https://mail.mozilla.org/listinfo/es-discuss
>> Allen Wirfs-Brock <mailto:[email protected]>
>> November 10, 2013 7:12 PM
>>
>> One of the the few remaining uses of a function's 'arguments' binding is
>> to determine the actual number of passed arguments. This is necessary in
>> some overloading scenarios where a function has different behavior when an
>> argument is completely absent then it has when undefined (or any other
>> default value) is explicitly passed in that parameter position. That
>> situation occurs in a number of DOM APIs and even a few ES library
>> functions.
>>
>> For example(see https://bugs.ecmascript.org/show_bug.cgi?id=1877 ),
>> Array.prototype.splice returns different results for:
>> [1,2,3].splice()
>> and
>> [1,2,3].splice(undefined)
>>
>> The natural ES6 declaration for a splice function is:
>>
>> function splice(start, deleteCount, ...items) {...
>>
>> but if you write it this way then within the body you have to have a test
>> like:
>>
>> if (arguments.length == 0) {...
>>
>> to implement the correct web-compatable behavior.
>>
>> Or, alternatively you could declare the functions as:
>>
>> function splice(...actualArgs) {
>> let [start, stop, ...item] = actualArgs;
>> ...
>> if (actualArgs.length == 0) {...
>>
>> So, to implement a Web-compaable version of splice you either have to use
>> 'arguments' to determine the actual number of passed objects or you need to
>> declare it with a bogus parameter pattern and use explicit or implicit
>> destructuring to parse out the positional parameters.
>>
>> One way around this dilemma would be to provide a syntactic affordance
>> for determing the actual argument count. For example, one possibility
>> would be to allow the last item of any formal parameter list to be an item
>> of the syntactic form:
>>
>> ActualArgumentCount : '#' BindingIdentifier
>>
>> So, the declaration for splice could then be:
>>
>> function splice(start, deleteCount, ...items, #argCount) {
>> ...
>> if (argCount == 0) {...
>>
>> Thoughts?
>>
>> Allen
>>
>>
>> _______________________________________________
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>> [email protected]
>> https://mail.mozilla.org/listinfo/es-discuss
>>
>
--
Cheers,
--MarkM
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