Editorial: Clarify identity as from perspective of spec vs language #3027

syg · 2023-03-09T00:28:41Z

This 2-level stratification of identity is needed rigor for Symbols as WeakMap keys (#2777) to capture the reason for why Symbol.for symbols cannot be used as weak targets.

spec.html

ljharb · 2023-03-16T22:33:59Z

spec.html

-      <p>A value without identity is never equal to a value with identity.</p>
+      <p>In this specification, both specification values and ECMAScript language values are compared for equality. When comparing for equality, values fall into one of two categories. <dfn variants="values without identity,value without identity">Values without identity</dfn> are equal to other values without identity if all of their innate characteristics are the same — characteristics such as the magnitude of an integer or the length of a sequence. Values without identity may be manifest without prior reference by fully describing their characteristics. In contrast, each <dfn variants="values with identity">value with identity</dfn> is unique and therefore only equal to itself. Values with identity are like values without identity but with an additional unguessable, unchangeable, universally-unique characteristic called <em>identity</em>. References to existing values with identity cannot be manifest simply by describing them, as the identity itself is indescribable; instead, references to these values must be explicitly passed from one place to another. Some values with identity are mutable and therefore can have their characteristics (except their identity) changed in-place, causing all holders of the value to observe the new characteristics. A value without identity is never equal to a value with identity.</p>
+      <p>From the perspective of this specification, the word “is” is used to compare two values for equality, as in “If _bool_ is *true*, then ...”, and the word “contains” is used to search for a value inside lists using equality comparisons, as in "If _list_ contains a Record _r_ such that _r_.[[Foo]] is *true*, then ...". The <em>specification identity</em> of values determines the result of these comparisons and is axiomatic in this specification.</p>
+      <p>From the perspective of the ECMAScript language, language values are compared for equality using the SameValue abstract operation and the abstract operations it transitively calls. The algorithms of these comparison abstract operations determine <em>language identity</em> of ECMAScript language values.</p>


i'd strongly prefer this to be dfn-d, but obv landing this is more important than addressing that even if editors preferred to, so it can be addressed later if needed.

syg · 2023-03-16T22:49:37Z

Please squash when merging, @ljharb, thanks.

This 2-level stratification of identity is needed rigor for Symbols as WeakMap keys (tc39#2777) to capture the reason for why Symbol.for symbols cannot be used as weak targets.

spec.html

This 2-level stratification of identity is needed rigor for Symbols as WeakMap keys (tc39#2777) to capture the reason for why Symbol.for symbols cannot be used as weak targets.

syg added editorial change editor call to be discussed in the next editor call labels Mar 9, 2023

syg requested a review from a team March 9, 2023 00:28

syg mentioned this pull request Mar 9, 2023

Normative: Permit Symbols as WeakMap keys #2777

Merged

syg force-pushed the stratified-identity branch from fdebad9 to c6621b4 Compare March 15, 2023 23:13

syg changed the title ~~Editorial: Split identity into spec and language identity~~ Editorial: Clarify identity as from perspective of spec vs language Mar 15, 2023

bakkot reviewed Mar 15, 2023

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