util: simplify constructor retrieval in inspect()

[Trott]

Instead of looping through a list of typed arrays, use
TypedArrayPrototypeGetSymbolToStringTag.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/34881/

[ExE-Boss]

This should probably use:

Suggested change

	let fallback = '';
	if (constructor === null) {
	const constr = findTypedConstructor(value);
	fallback = constr.name;
	fallback = TypedArrayPrototypeGetSymbolToStringTag(value);
	const fallback = TypedArrayPrototypeGetSymbolToStringTag(value);
	if (constructor === null) {

So that fallback is always non‑empty.

[Trott]

I think the idea originally was to avoid the overhead of a function call where possible. Judging from our test coverage stats, constructor being null is the unusual case (616 times hitting the if but only 33 times evaluating to true).

The performance difference seems likely to be unmeasurable and the code simplification may very well be worth it. But I'd prefer that be handled in a separate pull request. I'd prefer that this pull request preserve the code shape and merely replace/eliminate the existing function.

This is reminding me to run benchmarks for this change.

[ExE-Boss]

Well, TypedArrayPrototypeGetSymbolToStringTag is already invoked by isTypedArray:

node/lib/internal/util/types.js

Lines 8 to 10 in 72b07e4

	function isTypedArray(value) {
	return TypedArrayPrototypeGetSymbolToStringTag(value) !== undefined;
	}

---

It should be possible to reduce this to always perform only one TypedArrayPrototypeGetSymbolToStringTag call, even in the constructor === null case, but that is probably overkill:

   if (value[SymbolIterator] || constructor === null) {
     noIterator = false;
+    let typedArrayName;
     if (ArrayIsArray(value)) {

-    } else if (isTypedArray(name)) {
+    } else if ((typedArrayName = TypedArrayPrototypeGetSymbolToStringTag(value)) !== undefined) {
       keys = getOwnNonIndexProperties(value, filter);
       let bound = value;
-      let fallback = '';
       if (constructor === null) {
-        fallback = TypedArrayPrototypeGetSymbolToStringTag(value);
         // Reconstruct the array information.
-        bound = new primordials[primordials](value);
+        bound = new primordials[typedArrayName](value);
       }
       const size = TypedArrayPrototypeGetLength(value);
-      const prefix = getPrefix(constructor, tag, fallback, `(${size})`);
+      const prefix = getPrefix(constructor, tag, typedArrayName, `(${size})`);

[Trott]

Benchmark: https://ci.nodejs.org/view/Node.js%20benchmark/job/benchmark-node-micro-benchmarks/755/

[Trott]

Benchmark results seem OK:

15:25:18  util/inspect.js option='colors' method='Date' n=20000                          *     -5.88 %       ±4.69% ±6.26%  ±8.21%
15:25:18  util/inspect.js option='none' method='Object_deep_ln' n=20000                 **     -3.26 %       ±2.29% ±3.05%  ±3.97%
15:25:18  util/inspect.js option='none' method='Object_empty' n=20000                    *      4.28 %       ±3.82% ±5.10%  ±6.67%

15:25:18 Be aware that when doing many comparisons the risk of a false-positive
15:25:18 result increases. In this case there are 51 comparisons, you can thus
15:25:18 expect the following amount of false-positive results:
15:25:18   2.55 false positives, when considering a   5% risk acceptance (*, **, ***),
15:25:18   0.51 false positives, when considering a   1% risk acceptance (**, ***),
15:25:18   0.05 false positives, when considering a 0.1% risk acceptance (***)

15:25:18                                                                        confidence improvement accuracy (*)   (**)   (***)
15:25:18  util/inspect-array.js type='denseArray' len=100000 n=500                              0.67 %       ±5.34% ±7.11%  ±9.27%
15:25:18  util/inspect-array.js type='denseArray' len=100 n=500                                 1.13 %       ±3.89% ±5.18%  ±6.75%
15:25:18  util/inspect-array.js type='denseArray_showHidden' len=100000 n=500                   0.83 %       ±4.61% ±6.13%  ±7.98%
15:25:18  util/inspect-array.js type='denseArray_showHidden' len=100 n=500                      1.31 %       ±3.81% ±5.07%  ±6.60%
15:25:18  util/inspect-array.js type='mixedArray' len=100000 n=500                             -0.05 %       ±2.47% ±3.29%  ±4.28%
15:25:18  util/inspect-array.js type='mixedArray' len=100 n=500                                 1.01 %       ±3.89% ±5.18%  ±6.74%
15:25:18  util/inspect-array.js type='sparseArray' len=100000 n=500                            -0.15 %       ±4.16% ±5.53%  ±7.20%
15:25:18  util/inspect-array.js type='sparseArray' len=100 n=500                                1.18 %       ±4.34% ±5.79%  ±7.56%
15:25:18  util/inspect.js option='colors' method='Array' n=20000                                0.61 %       ±2.10% ±2.80%  ±3.64%
15:25:18  util/inspect.js option='colors' method='Date' n=20000                          *     -5.88 %       ±4.69% ±6.26%  ±8.21%
15:25:18  util/inspect.js option='colors' method='Error' n=20000                               -1.18 %       ±3.79% ±5.04%  ±6.57%
15:25:18  util/inspect.js option='colors' method='Number' n=20000                              -1.30 %       ±3.98% ±5.31%  ±6.93%
15:25:18  util/inspect.js option='colors' method='Object_deep_ln' n=20000                       0.58 %       ±1.67% ±2.23%  ±2.90%
15:25:18  util/inspect.js option='colors' method='Object_empty' n=20000                         0.53 %       ±4.28% ±5.70%  ±7.41%
15:25:18  util/inspect.js option='colors' method='Object' n=20000                               1.21 %       ±3.56% ±4.74%  ±6.17%
15:25:18  util/inspect.js option='colors' method='Set' n=20000                                 -3.47 %       ±4.67% ±6.22%  ±8.10%
15:25:18  util/inspect.js option='colors' method='String_boxed' n=20000                         0.08 %       ±4.51% ±6.00%  ±7.82%
15:25:18  util/inspect.js option='colors' method='String_complex' n=20000                       1.16 %       ±4.39% ±5.83%  ±7.59%
15:25:18  util/inspect.js option='colors' method='String' n=20000                               0.67 %       ±4.67% ±6.21%  ±8.10%
15:25:18  util/inspect.js option='colors' method='TypedArray_extra' n=20000                     1.33 %       ±2.18% ±2.90%  ±3.77%
15:25:18  util/inspect.js option='colors' method='TypedArray' n=20000                           1.12 %       ±1.87% ±2.49%  ±3.24%
15:25:18  util/inspect.js option='none' method='Array' n=20000                                  2.63 %       ±6.13% ±8.19% ±10.71%
15:25:18  util/inspect.js option='none' method='Date' n=20000                                  -3.11 %       ±4.32% ±5.76%  ±7.50%
15:25:18  util/inspect.js option='none' method='Error' n=20000                                 -0.57 %       ±3.73% ±4.96%  ±6.45%
15:25:18  util/inspect.js option='none' method='Number' n=20000                                 0.99 %       ±3.42% ±4.55%  ±5.92%
15:25:18  util/inspect.js option='none' method='Object_deep_ln' n=20000                 **     -3.26 %       ±2.29% ±3.05%  ±3.97%
15:25:18  util/inspect.js option='none' method='Object_empty' n=20000                    *      4.28 %       ±3.82% ±5.10%  ±6.67%
15:25:18  util/inspect.js option='none' method='Object' n=20000                                 2.62 %       ±5.11% ±6.80%  ±8.86%
15:25:18  util/inspect.js option='none' method='Set' n=20000                                   -2.91 %       ±4.79% ±6.38%  ±8.31%
15:25:18  util/inspect.js option='none' method='String_boxed' n=20000                          -2.02 %       ±3.95% ±5.27%  ±6.89%
15:25:18  util/inspect.js option='none' method='String_complex' n=20000                         1.76 %       ±5.12% ±6.82%  ±8.87%
15:25:18  util/inspect.js option='none' method='String' n=20000                                -2.11 %       ±4.35% ±5.79%  ±7.54%
15:25:18  util/inspect.js option='none' method='TypedArray_extra' n=20000                      -3.93 %       ±6.05% ±8.14% ±10.78%
15:25:18  util/inspect.js option='none' method='TypedArray' n=20000                            -2.44 %       ±4.85% ±6.51%  ±8.61%
15:25:18  util/inspect.js option='showHidden' method='Array' n=20000                           -0.67 %       ±4.44% ±5.96%  ±7.88%
15:25:18  util/inspect.js option='showHidden' method='Date' n=20000                            -2.07 %       ±4.13% ±5.51%  ±7.20%
15:25:18  util/inspect.js option='showHidden' method='Error' n=20000                           -2.60 %       ±3.77% ±5.04%  ±6.60%
15:25:18  util/inspect.js option='showHidden' method='Number' n=20000                           0.55 %       ±4.56% ±6.06%  ±7.90%
15:25:18  util/inspect.js option='showHidden' method='Object_deep_ln' n=20000                  -0.64 %       ±2.50% ±3.33%  ±4.34%
15:25:18  util/inspect.js option='showHidden' method='Object_empty' n=20000                     1.53 %       ±4.64% ±6.18%  ±8.06%
15:25:18  util/inspect.js option='showHidden' method='Object' n=20000                          -1.09 %       ±4.44% ±5.91%  ±7.70%
15:25:18  util/inspect.js option='showHidden' method='Set' n=20000                              1.38 %       ±5.30% ±7.05%  ±9.18%
15:25:18  util/inspect.js option='showHidden' method='String_boxed' n=20000                     1.11 %       ±3.77% ±5.02%  ±6.54%
15:25:18  util/inspect.js option='showHidden' method='String_complex' n=20000                  -0.27 %       ±4.27% ±5.68%  ±7.39%
15:25:18  util/inspect.js option='showHidden' method='String' n=20000                          -3.13 %       ±3.14% ±4.18%  ±5.44%
15:25:18  util/inspect.js option='showHidden' method='TypedArray_extra' n=20000                -0.59 %       ±2.55% ±3.41%  ±4.45%
15:25:18  util/inspect.js option='showHidden' method='TypedArray' n=20000                       0.83 %       ±2.14% ±2.85%  ±3.71%
15:25:18  util/inspect-proxy.js isProxy=0 showProxy=0 n=100000                                 -1.60 %       ±3.81% ±5.11%  ±6.72%
15:25:18  util/inspect-proxy.js isProxy=0 showProxy=1 n=100000                                  0.90 %       ±1.58% ±2.11%  ±2.75%
15:25:18  util/inspect-proxy.js isProxy=1 showProxy=0 n=100000                                 -0.70 %       ±2.52% ±3.36%  ±4.38%
15:25:18  util/inspect-proxy.js isProxy=1 showProxy=1 n=100000                                  1.51 %       ±2.50% ±3.35%  ±4.39%
15:25:18 
15:25:18 Be aware that when doing many comparisons the risk of a false-positive
15:25:18 result increases. In this case there are 51 comparisons, you can thus
15:25:18 expect the following amount of false-positive results:
15:25:18   2.55 false positives, when considering a   5% risk acceptance (*, **, ***),
15:25:18   0.51 false positives, when considering a   1% risk acceptance (**, ***),
15:25:18   0.05 false positives, when considering a 0.1% risk acceptance (***)

[Trott]

Landed in f43d1ca