New private names proposal

[Mark S. Miller]

On Wed, Dec 22, 2010 at 11:56 AM, Mark S. Miller <erights at google.com> wrote:

> On Tue, Dec 21, 2010 at 2:44 PM, Allen Wirfs-Brock <allen at wirfs-brock.com>
>  wrote:
>
>>
>> Please don't totally disengage from the syntax discussion.  Most
>> programmers understanding of the language starts with the concrete (syntax)
>> and then proceeds to the abstract (semantics).  Syntax design can have a big
>> impact on the usability of the underlying semantics
>>
>
>
> Ok, I am not sure what I think of the following idea, but it's a bit
> different in flavor and so may stimulate other thoughts. I will express the
> expansion in terms of the natural expansion for a soft fields underpinning.
> One could do an equally natural expansion for private names. "==>" means
> "expands to". Actual expansions would be a bit more complex to preserve the
> left-to-right order of evaluation of the original.
>
> The basic idea is, since we're considering a sigil anyway, and since .# and
> [# would both treat the thing to their right as something to be evaluated,
> why not turn the sigil into an infix operator instead? Then it can be used
> as "."-like "[]"-like without extra notation or being too closely confused
> with "." or "[]" themselves. Finally, given the meaning of the sigil-turned
> operator, "@" seemed to read better to me than "#". YMMV.
>
>
>       expr1 @ expr2
> ==>
>       expr2.get(expr1)
>
>       expr1 @ expr2 = expr3;
> ==>
>       expr2.set(expr1, expr3);
>
>       const obj = {@expr1: expr2, ...};
> ==>
>       const obj = {...}; expr1.set(obj, expr2);
>
>
> Perhaps the expression on the right need not be a Name/SoftField. It could
> be anything that responds to "get" and "set".
>
>
Redoing the "class private" example at the end of
http://wiki.ecmascript.org/doku.php?id=strawman:private_names#using_private_identifiers
http://wiki.ecmascript.org/doku.php?id=strawman:names_vs_soft_fields#using_private_identifiers


const key = SoftField();  // or, obviously, Name(),
depending...function Thing() {
    this @ key = "class private value";
    this.hasKey = function(x) {
        return x @ key === this @ key;
    };
    this.getThingKey = function(x) {
        return x @ key;
    };}
 var thing1 = new Thing;var thing2 = new Thing;
 print("key" in thing1);       // falseprint(thing1.hasKey(thing1));
// trueprint(thing1.hasKey(thing2)); // true





-- 
    Cheers,
    --MarkM
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