Reduce ThicknessConverter allocs to minimum and improve conversion performance

[h3xds1nz]

Description

Simplifies code in CanConvertTo/ConvertFrom/ConvertTo, removes additional type casts by using is checks/pattern match. Commits should be easy to review.

Uses DefaultInterpolatedStringHandler instead of StringBuilder to handle conversion in ToString with a pre-allocated on-stack buffer (not using interpolated strings directly due to the NaN->Auto conversion which would box as Roslyn won't handle that one.

Also stackallocs 4 doubles instead of allocating an array in FromString, this uses unsafe quotation due to how the current code-gen with Span looks like; additional perf improvement. I didn't include benchmark/tests in this one, they're together in the other PR for LengthConverter #9364.

Multiple decimals point (edge case but within original range)

ToString(new Thickness(3.33371, 2.25888, 6.6666, 8.444), CultureInfo.InvariantCulture);

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Allocated [B]
PR_EDIT	348.2 ns	2.56 ns	2.27 ns	0.0048	80 B
Original	393.2 ns	3.05 ns	2.70 ns	0.0257	432 B

Single decimal point, standard use-case

ToString(new Thickness(1, 2, 2.5, 4), CultureInfo.InvariantCulture);

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Allocated [B]
PR_EDIT	277.4 ns	2.22 ns	2.08 ns	0.0024	40 B
Original	328.1 ns	4.37 ns	4.09 ns	0.0205	344 B

Conversion from double.NaN to Auto

ToString(new Thickness(double.NaN), CultureInfo.InvariantCulture);

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Allocated [B]
PR_EDIT	24.23 ns	0.187 ns	0.146 ns	0.0038	64 B
Original	32.90 ns	0.441 ns	0.391 ns	0.0157	264 B

Customer Impact

Improved performance, greatly decreased allocations.

Regression

No.

Testing

Local build, basic set of assert testing.

CultureInfo CachedNorwegian = new CultureInfo("nn-NO");

Assert.AreEqual(ToString(new Thickness(1.5, 2, 1.25, 3), CultureInfo.InvariantCulture), ToString2(new Thickness(1.5, 2, 1.25, 3), CultureInfo.InvariantCulture));
Assert.AreEqual(ToString(new Thickness(3, 2, 6, 8), CultureInfo.InvariantCulture), ToString2(new Thickness(3, 2, 6, 8), CultureInfo.InvariantCulture));
Assert.AreEqual(ToString(new Thickness(3.33371, 2.25888, 6.6666, 8.444), CultureInfo.InvariantCulture), ToString2(new Thickness(3.33371, 2.25888, 6.6666, 8.444), CultureInfo.InvariantCulture));

//Culture with decimal comma separator
Assert.AreEqual(ToString(new Thickness(1.5, 2, 1.25, 3), CachedNorwegian), ToString2(new Thickness(1.5, 2, 1.25, 3), CachedNorwegian));
Assert.AreEqual(ToString(new Thickness(3, 2, 6, 8), CachedNorwegian), ToString2(new Thickness(3, 2, 6, 8), CachedNorwegian));
Assert.AreEqual(ToString(new Thickness(3.33371, 2.25888, 6.6666, 8.444), CachedNorwegian), ToString2(new Thickness(3.33371, 2.25888, 6.6666, 8.444), CachedNorwegian));

Assert.AreEqual(ToString(new Thickness(), CachedNorwegian), ToString2(new Thickness(), CachedNorwegian));

Assert.AreEqual(ToString(new Thickness(double.NaN), CachedNorwegian), ToString2(new Thickness(double.NaN), CachedNorwegian));

Risk

Low.

Microsoft Reviewers: Open in CodeFlow