Editorial: Using is -0 instead of = -0 in StringGetOwnProperty

[jhnaldo]

I revised a small part in StringGetOwnProperty to use is -0 instead of = -0 to correctly represent the semantics. The expression index = -0 denotes that index is -0 or +0 because the = operator is floating point equality operator. Thus, instead, I think that it should be revised to index is -0.

[ljharb]

There's a few other cases of = 0; we should probably change all of them at once to be "is 0".

(Also, note the overlap with #1086)

[jhnaldo]

There's a few other cases of = 0; we should probably change all of them at once to be "is 0".

(Also, note the overlap with #1086)

I'm confusing to understand the conversations in #1086.
So, in consequence, what is the exact meaning of = 0 and is 0?
I believe that the meaning is as follows:

• x = 0 denotes x is ES Number values +0, -0, or the mathematical value 0
• x is 0 denotes x should be mathematical value 0.

Am I right?

[ljharb]

In general, there's a lot of implicitness around Number and mathematical values in the spec; this seems like it may be one of those cases.

[jhnaldo]

@ljharb I think that = -0 and = 0 cases are slightly different. I don't know whether few cases of = 0 are correct or not, or even if they are incorrect, I don't know how to revise them.

However, I believe that the = -0 equality check in StringGetOwnProperty should revised into is -0.
According to #1752, it revised = -0 equality check to use instead is 0 and it was accepted and merged. Is there other issues that only this = -0 equality check should be considered with other cases of = 0?

[littledan]

This seems like a good fix to me. In the scheme of things like = relating to mathematical values, I see = -0 being the same as = 0, whereas is implies SameValue. @caiolima is working on a fixup for mathematical values in general based on discussion in #1964 ; I'd be fine with either waiting for that or landing this independently.

[bakkot]

I am in favor of this change. Specifically, for the case of comparing ECMAScript values to the ECMAScript values 0 and -0 I would prefer that we always say is +0 or is -0 rather than = 0, = +0, = -0, or is 0.