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make @@toStringTag and constructor prototype properties funky accessors #287

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Dec 4, 2023
Merged

make @@toStringTag and constructor prototype properties funky accessors #287

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e298671
make @@toStringTag and constructor prototype properties funky accessors
michaelficarra Sep 18, 2023
f481720
throw instead of silently doing nothing
michaelficarra Oct 12, 2023
7d48c43
throw when this value is Iterator.prototype
michaelficarra Oct 12, 2023
d741076
rewrite funky setter and extract as an AO
michaelficarra Oct 17, 2023
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59 changes: 56 additions & 3 deletions spec.html
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Original file line number Diff line number Diff line change
Expand Up @@ -289,7 +289,35 @@ <h1>Iterator.prototype</h1>

<emu-clause id="sec-iteratorprototype.constructor">
<h1>Iterator.prototype.constructor</h1>
<p>The initial value of %Iterator.prototype%.constructor is %Iterator%.</p>
<p>`Iterator.prototype.constructor` is an accessor property with attributes { [[Enumerable]]: *false*, [[Configurable]]: *true* }. The [[Get]] and [[Set]] attributes are defined as follows:</p>

<emu-clause id="sec-get-iteratorprototype-constructor">
<h1>get Iterator.prototype.constructor</h1>
<p>The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:</p>
<emu-alg>
1. Return %Iterator%.
</emu-alg>
</emu-clause>

<emu-clause id="sec-set-iteratorprototype-constructor">
<h1>set Iterator.prototype.constructor</h1>
<p>The value of the [[Set]] attribute is a built-in function that takes an argument _v_. It performs the following steps when called:</p>
<emu-alg>
1. Let _O_ be ? RequireObjectCoercible(*this* value).
1. If _O_ is %Iterator.prototype%, then
1. Return *undefined*.
1. Let _desc_ be ? _O_.[[GetOwnProperty]](*"constructor"*).
1. If IsDataDescriptor(_desc_) is *true* and _desc_.[[Writable]] is *false*, then
1. Return *undefined*.
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@bakkot bakkot Sep 26, 2023 •
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Per request of @erights this should be an error, to emulate strict rather than sloppy assignment.

1. Let _newDesc_ be the PropertyDescriptor { [[Value]]: _v_, [[Writable]]: *true*, [[Enumerable]]: *false*, [[Configurable]]: *true* }.
1. Perform ? _O_.[[DefineOwnProperty]](*"constructor"*, _newDesc_).
1. Return *undefined*.
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if we're really going to do this it should be an AO that many things can share, since the only things that potentially change are Iterator.prototype and the property name

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that can be an editorial thing we address in the PR to 262

</emu-alg>
</emu-clause>

<emu-note>
<p>Unlike the *"constructor"* property on most built-in prototypes, for web-compatibility reasons this property must be an accessor.</p>
</emu-note>
</emu-clause>

<emu-clause id="sec-iteratorprototype.map">
Expand Down Expand Up @@ -563,9 +591,34 @@ <h1>Iterator.prototype.find ( _predicate_ )</h1>

<emu-clause id="sec-iteratorprototype-@@tostringtag">
<h1>Iterator.prototype [ @@toStringTag ]</h1>
<p>The initial value of the @@toStringTag property is the String value "Iterator".</p>
<p>`Iterator.prototype[@@toStringTag]` is an accessor property with attributes { [[Enumerable]]: *false*, [[Configurable]]: *true* }. The [[Get]] and [[Set]] attributes are defined as follows:</p>

<emu-clause id="sec-get-iteratorprototype-@@tostringtag">
<h1>get Iterator.prototype [ @@toStringTag ]</h1>
<p>The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:</p>
<emu-alg>
1. Return *"Iterator"*.
</emu-alg>
</emu-clause>

<emu-clause id="sec-set-iteratorprototype-@@tostringtag">
<h1>set Iterator.prototype [ @@toStringTag ]</h1>
<p>The value of the [[Set]] attribute is a built-in function that takes an argument _v_. It performs the following steps when called:</p>
<emu-alg>
1. Let _O_ be ? RequireObjectCoercible(*this* value).
1. If _O_ is %Iterator.prototype%, then
1. Return *undefined*.
1. Let _desc_ be ? _O_.[[GetOwnProperty]](@@toStringTag).
1. If IsDataDescriptor(_desc_) is *true* and _desc_.[[Writable]] is *false*, then
1. Return *undefined*.
1. Let _newDesc_ be the PropertyDescriptor { [[Value]]: _v_, [[Writable]]: *true*, [[Enumerable]]: *false*, [[Configurable]]: *true* }.
1. Perform ? _O_.[[DefineOwnProperty]](@@toStringTag, _newDesc_).
1. Return *undefined*.
</emu-alg>
</emu-clause>

<emu-note>
<p>Unlike the @@toStringTag on most built-in classes, for web-compatibility reasons this property must be writable.</p>
<p>Unlike the @@toStringTag property on most built-in prototypes, for web-compatibility reasons this property must be an accessor.</p>
</emu-note>
</emu-clause>
</emu-clause>
Expand Down
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