Arrow binding

David Herman dherman at
Tue Apr 24 14:54:37 PDT 2012

On Apr 24, 2012, at 2:09 PM, Allen Wirfs-Brock wrote:

> On Apr 24, 2012, at 1:40 PM, David Herman wrote:
>> On Apr 24, 2012, at 10:03 AM, Tab Atkins Jr. wrote:
>>> There doesn't seem to be a need there for thin-arrow (dynamic this) functions.
>>> (Edit: Oh, I see, leaning on the completion value of thin-arrow
>>> functions here lets you shave a few characters off.  The readability
>>> loss of mixing the two syntaxes doesn't seem worthwhile, though.)
>> Lets you eliminate "{" and "}" and "return", but requires additional ":" and "->". Net savings of 3 characters. But more than that, eliminating "return" lets you write methods in a functional style without needing the explicit control flow operator.
> I believe that we could grammatically use ArrowBody as the body of concise methods in object literals and classes.  In that case, Dave's example could be expressed as:
>     box = {
>         _value: 0,
>         unbox() ()-> this._value,


    unbox() this._value,

>         setbox(v)  this._value = v 
>     }
> It could also be used as the body of getter/setters
>     val = {
>         _value: 0,
>         get value() this._value,
>         set value(v)  this._value = v 
>     }

This all seems reasonable to me. I guess I see a couple reasonable alternatives here:

A. add thin arrow, add expression bodies to method shorthands

    (-) Might be a bit much
    (+) But all around a goodly set of convenience forms

B. add expression bodies to method shorthands, don't add skinny arrow

    (-) Loses the flexibility of shorthand syntax for assigning to an existing object, a Tab pointed out. (Sorry Axel, mustache is not particularly Harmonious.)
    (+) Keeps us to just one arrow form

C. eliminate method shorthands, add skinny arrow

    (-) Loses the method shorthand in object literals
    (-) Methods in classes would remain the same, which loses some symmetry between object literals and classes
    (+) Eliminates visual confusion between getters/setters and method shorthand, but still with a minimal syntax (i.e., "->")

All three of these options look pretty decent to me. I think I'd be pretty happy with any of them.


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