An element of a programming that has its own distinct syntax rules is sometimes called a “special form”. So … can be called a special form. Or you can think of it as an syntactic element of argument lists, parameter lists, array literals/destructuring, object literals/destructuring, each of which is itself a special form.
> On Jul 5, 2017, at 6:32 AM, Andrew Li <[email protected]> wrote: > > I hadn't though about rest and how it passes multiple values to a function -- > so it's definitely not an operator. I would say that since spread/rest syntax > doesn't always evaluate to exactly one value, is context-specific (you can't > use it standalone), and isn't defined as an operator in the ECMAScript spec > with productions only ever containing *literally* ..., I can say definitively > that it's not an operator. > > On Wed, Jul 5, 2017 at 7:59 AM, T.J. Crowder <[email protected] > <mailto:[email protected]>> wrote: > You're not alone in this question; early on, lots of folks called `...` an > operator. It isn't. Rest and spread are syntax, just like the commas in a > function's parameter declaration list are syntax, not the comma operator. > What rest and spread do is outside the realm of what an operator can do. An > operator has a *single* result value which is (optionally) used where the > operator's expression was once the expression has been evaluated. E.g., in > `foo(2 * 5)`, the `2 * 5` is evaluated and the resulting value (`10`) is > passed into `foo` as the first argument. Roughly speaking, operators are > built-in functions with A) optionally-symbolic names, B) infix notation (for > binary and ternary operators), and C) lazy argument evaluation; and like > functions, they have only a single result value (and potential side-effects). > Rest and spread can't be expressed that way. Consider `foo(...a)`. There's no > single result value there, there's a series of discrete values used as > discrete arguments to `foo`. > > -- T.J. Crowder > > On Wed, Jul 5, 2017 at 1:40 PM, Andrew Li <[email protected] > <mailto:[email protected]>> wrote: > It seems as if there's two different ways to refer to the ... punctuator. How > should I refer to this: > > const foo = [bar, ...baz]; > > MDN seems to suggest it's referred to as 'spread syntax' but its article URL > seems to suggest it was initially created under the name 'spread operator' -- > and it's more popular when looking at Google results. Syntax is the 'form' of > the language while operators are generally used to perform a certain > operation on a number of operands to produce a value. > > It seems as if on the surface, 'operator' is the most appropriate fit here, > as it's seems more like a prefix unary operator more than it is syntax. But > in the context of ECMAScript, it's not listed as an operator at MDN nor > explicitly in the language specification -- and it's more of an extension of > array literal syntax and only works in context of array literals. I would say > it's more appropriately named syntax due to that, in the language > specification, it's only ever mentioned literally in the ArgumentList and > SpreadELement productions. That seems to suggest it's more just syntax rather > than a standalone operator such as + or *. > > Which way of referring to it would be more 'correct' if any and is my > reasoning correct? > > _______________________________________________ > es-discuss mailing list > [email protected] <mailto:[email protected]> > https://mail.mozilla.org/listinfo/es-discuss > <https://mail.mozilla.org/listinfo/es-discuss> > > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss
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