Replace CaseInsensitiveComparer with generics in Speller, remove allocations

[h3xds1nz]

Description

Replaces CaseInsensitiveComparer with IComparer<string> interface (StringComparer). Also replaces ArrayList with generic List<string> for minor perf benefit and increased code quality.

• The IComparer<string> is now stored as a readonly variable in Speller, removing constant comparer allocs on segment checks.
• Also removes unnecessary char[] allocation/copy and its immediate conversion to string, skipping one whole alloc round.
• Keeps the initial capacity of 1 for the list, the subsequent sorted insertions are not a bottleneck for this use-case.

I've created a very rough typical use-case benchmark that's not gonna be 100% time-accurate but the time itself isn't important, allocs are (should mimic the previous/new code).

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	163,420.2 ns	1,550.7 ns	1,450.5 ns	6.1035	10,976 B	104576 B
PR__EDIT	154,813.4 ns	1,272.3 ns	1,190.1 ns	2.1973	5,332 B	40000 B

Benchmark code

private ArrayList _alIgnoredWords;
private List<string> _ignoredList;

private readonly CultureInfo _defaultCulture; //CultureInfo.CurrentCulture;
private readonly IComparer<string> _defaultComparer; //StringComparer.Create(_defaultCulture, true);

private readonly static char[] oldHannah =  { 'h', 'a', 'n', 'n', 'a', 'h' };

[Benchmark]
public void Original()
{
    //Add some items
    IgnoreAll("hell");
    IgnoreAll("aleela");
    IgnoreAll("anna");
    IgnoreAll("hannah");
    IgnoreAll("vaka");
    IgnoreAll("cute");
    IgnoreAll("he2ll");
    IgnoreAll("al2eela");
    IgnoreAll("an2na");
    IgnoreAll("han2nah");
    IgnoreAll("vak2a");
    IgnoreAll("cu2te");
    IgnoreAll("hell4");
    IgnoreAll("aleela4");
    IgnoreAll("anna4");
    IgnoreAll("hannah4");
    IgnoreAll("vaka4");
    IgnoreAll("cute4");
    IgnoreAll("he2ll4");
    IgnoreAll("al2eela4");
    IgnoreAll("an2na4");
    IgnoreAll("han2nah4");
    IgnoreAll("vak2a4");
    IgnoreAll("cu2te4");

    //Let's run some scans
    for (int i = 0; i < 1_000; i++)
    {
        char[] word = { 'h', 'a', 'n', 'n', 'a', 'h'};
        IsIgnoredWord(word);
    }
}
[Benchmark]
public void PR__EDIT()
{
    //Add some items
    IgnoreAllV2("hell");
    IgnoreAllV2("aleela");
    IgnoreAllV2("anna");
    IgnoreAllV2("hannah");
    IgnoreAllV2("vaka");
    IgnoreAllV2("cute");
    IgnoreAllV2("he2ll");
    IgnoreAllV2("al2eela");
    IgnoreAllV2("an2na");
    IgnoreAllV2("han2nah");
    IgnoreAllV2("vak2a");
    IgnoreAllV2("cu2te");
    IgnoreAllV2("hell4");
    IgnoreAllV2("aleela4");
    IgnoreAllV2("anna4");
    IgnoreAllV2("hannah4");
    IgnoreAllV2("vaka4");
    IgnoreAllV2("cute4");
    IgnoreAllV2("he2ll4");
    IgnoreAllV2("al2eela4");
    IgnoreAllV2("an2na4");
    IgnoreAllV2("han2nah4");
    IgnoreAllV2("vak2a4");
    IgnoreAllV2("cu2te4");

    //Let's run some scans
    for (int i = 0; i < 1_000; i++)
    {
        string word = new(oldHannah);
        IsIgnoredWordV2(word);
    }
}

private void IgnoreAll(string word)
{
    if (_alIgnoredWords is null)
        _alIgnoredWords = new ArrayList(1);

    int index = _alIgnoredWords.BinarySearch(word, new CaseInsensitiveComparer(_defaultCulture));

    if (index < 0)
    {
        _alIgnoredWords.Insert(~index, word);
    }
}

private bool IsIgnoredWord(char[] word) => _alIgnoredWords?.BinarySearch(new string(word), new CaseInsensitiveComparer(_defaultCulture)) >= 0;

private void IgnoreAllV2(string word)
{
    if (_ignoredList is null)
        _ignoredList = new List<string>(1);

    int index = _ignoredList.BinarySearch(word, _defaultComparer);

    if (index < 0)
    {
        _ignoredList.Insert(~index, word);
    }
}

private bool IsIgnoredWordV2(string word) => _ignoredList?.BinarySearch(word, _defaultComparer) >= 0;

Customer Impact

Increased performance, decreased allocations.

Regression

No.

Testing

Local build, base functionality.

Risk

Low.

Microsoft Reviewers: Open in CodeFlow

[singhashish-wpf]

Thanks @h3xds1nz for this contribution.

[h3xds1nz]

Thanks @singhashish-wpf for including it!