Match slices without materialising them when parsing

[twcclegg]

Two Substring calls on the parse path existed only to hand a slice to a regex:

• MaybeStripNationalPrefixAndCarrierCode — numberString.Substring(prefixMatch.Length) for an
  IsMatchAll check
• MaybeStripExtension — numberString.Substring(0, m.Index) for the viability check

On net7.0+ Regex.IsMatch(ReadOnlySpan<char>) means neither slice needs to become a string. Both
call sites now go through a small helper that holds the #if, so the parse logic itself reads the
same as before — this file is kept diffable against the upstream Java.

The PhoneRegex span overload is internal: a public one would exist on the net8.0 and net10.0
assets but not netstandard2.0, which is what package validation's cross-framework check polices.
Replacing the public string overloads outright is recorded on #375 for a major version.

These are the paths #381 made measurable — an E164 parse never reaches either, since both regexes
fail and cost nothing. Watch ParseNationalFormat and ParseWithExtension allocation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.01%. Comparing base (af40c92) to head (848dd21).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #382   +/-   ##
=======================================
  Coverage   98.01%   98.01%           
=======================================
  Files          39       39           
  Lines       52818    52821    +3     
  Branches     1105     1106    +1     
=======================================
+ Hits        51770    51773    +3     
  Misses        795      795           
  Partials      253      253           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

📊 Benchmark Results

Commit: 848dd21 · Full run · Linux ubuntu-24.04-arm

Both sides were measured on the same runner in the same job, so the numbers are
comparable. Treat sub-percent differences as noise.

PR branch

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
InputDigitPerKeystroke	1000	4.601 ms	0.0685 ms	0.0641 ms	54.6875	3.87 MB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]     : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  Job-AMQORM : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Runtime=.NET 10.0  InvocationCount=1  IterationCount=20  
LaunchCount=1  RunStrategy=ColdStart  UnrollFactor=1  
WarmupCount=1  

Method	Mean	Error	StdDev	Allocated
CreateInstance	413.3 μs	117.7 μs	135.5 μs	119.48 KB
CreateInstanceAndLoadAllRegions	7,081.2 μs	446.9 μs	514.6 μs	1619.1 KB
FirstRegionLookup	458.6 μs	142.1 μs	163.6 μs	124.54 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
ExtractPossibleNumber_CleanInput	1000	21.65 μs	0.027 μs	0.025 μs	-	-
ExtractPossibleNumber_WithLeadingJunk	1000	38.56 μs	0.071 μs	0.066 μs	0.6714	48360 B

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
FindNumbers_Valid	100	140.5 μs	0.24 μs	0.21 μs	0.9766	69.93 KB
FindNumbers_StrictGrouping	100	314.4 μs	0.75 μs	0.67 μs	1.4648	123.2 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
GetDescriptionForNumber	1000	1,502.35 μs	4.562 μs	4.044 μs	1.9531	196.63 KB
GetDisplayCountry	1000	24.87 μs	0.042 μs	0.039 μs	0.0916	7.56 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
ParseValidateAndFormatPhoneNumbers	1000	2,704.7 μs	16.50 μs	13.78 μs	7.8125	580.13 KB
ParseOnly	1000	436.2 μs	0.57 μs	0.51 μs	4.8828	350.55 KB
ParseNationalFormat	1000	846.6 μs	1.41 μs	1.18 μs	8.7891	581.22 KB
ParseWithExtension	1000	1,213.5 μs	1.90 μs	1.78 μs	21.4844	1405.12 KB
ValidateOnly	1000	779.2 μs	2.80 μs	2.48 μs	-	41.11 KB
FormatOnly	1000	1,123.1 μs	2.15 μs	1.90 μs	1.9531	187.92 KB

PR base

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
InputDigitPerKeystroke	1000	4.660 ms	0.0497 ms	0.0415 ms	54.6875	3.87 MB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]     : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  Job-AMQORM : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Runtime=.NET 10.0  InvocationCount=1  IterationCount=20  
LaunchCount=1  RunStrategy=ColdStart  UnrollFactor=1  
WarmupCount=1  

Method	Mean	Error	StdDev	Allocated
CreateInstance	423.6 μs	122.4 μs	140.9 μs	119.48 KB
CreateInstanceAndLoadAllRegions	7,103.9 μs	419.9 μs	483.6 μs	1619.1 KB
FirstRegionLookup	471.4 μs	147.4 μs	169.8 μs	124.54 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
ExtractPossibleNumber_CleanInput	1000	21.63 μs	0.020 μs	0.018 μs	-	-
ExtractPossibleNumber_WithLeadingJunk	1000	38.32 μs	0.058 μs	0.055 μs	0.6714	48360 B

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
FindNumbers_Valid	100	142.4 μs	0.22 μs	0.18 μs	0.9766	69.93 KB
FindNumbers_StrictGrouping	100	315.6 μs	0.72 μs	0.67 μs	1.4648	123.2 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
GetDescriptionForNumber	1000	1,484.30 μs	9.331 μs	8.728 μs	1.9531	196.63 KB
GetDisplayCountry	1000	21.33 μs	0.009 μs	0.007 μs	0.0916	7.56 KB

BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
Neoverse-N2, 4 physical cores
.NET SDK 10.0.302
  [Host]    : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a
  .NET 10.0 : .NET 10.0.10 (10.0.10, 10.0.1026.32716), Arm64 RyuJIT armv8.0-a

Job=.NET 10.0  Runtime=.NET 10.0  

Method	PhoneNumberCount	Mean	Error	StdDev	Gen0	Allocated
ParseValidateAndFormatPhoneNumbers	1000	2,967.0 μs	58.74 μs	126.43 μs	7.8125	580.51 KB
ParseOnly	1000	435.3 μs	0.62 μs	0.55 μs	4.8828	350.95 KB
ParseNationalFormat	1000	848.1 μs	2.78 μs	2.46 μs	8.7891	581.22 KB
ParseWithExtension	1000	1,217.4 μs	2.69 μs	2.25 μs	21.4844	1459.2 KB
ValidateOnly	1000	781.7 μs	2.39 μs	2.12 μs	-	41.11 KB
FormatOnly	1000	1,096.9 μs	2.32 μs	2.06 μs	1.9531	187.92 KB