【C#】string.StartsWith や string.EndsWith は引数に StringComparison.Ordinal を指定すると処理が速くなる

検証用スクリプト

using System;
using System.Diagnostics;
using UnityEngine;
using Debug = UnityEngine.Debug;

public class Example : MonoBehaviour
{
    public int m_count = 1_000_000;

    private void Start()
    {
        const string path          = "Assets/Example.cs";
        const string directoryName = "Assets/";
        const string extension     = ".cs";

        {
            var stopwatch = Stopwatch.StartNew();

            for ( var i = 0; i < m_count; i++ )
            {
                path.StartsWith( directoryName );
            }

            Debug.Log( $"path.StartsWith( directoryName ): {stopwatch.Elapsed.TotalSeconds} 秒 " );
        }

        {
            var stopwatch = Stopwatch.StartNew();

            for ( var i = 0; i < m_count; i++ )
            {
                path.StartsWith( directoryName, StringComparison.Ordinal );
            }

            Debug.Log( $"path.StartsWith( directoryName, StringComparison.Ordinal ): {stopwatch.Elapsed.TotalSeconds} 秒 " );
        }

        {
            var stopwatch = Stopwatch.StartNew();

            for ( var i = 0; i < m_count; i++ )
            {
                path.EndsWith( extension );
            }

            Debug.Log( $"path.EndsWith( extension ): {stopwatch.Elapsed.TotalSeconds} 秒 " );
        }

        {
            var stopwatch = Stopwatch.StartNew();

            for ( var i = 0; i < m_count; i++ )
            {
                path.EndsWith( extension, StringComparison.Ordinal );
            }

            Debug.Log( $"path.EndsWith( extension, StringComparison.Ordinal ): {stopwatch.Elapsed.TotalSeconds} 秒 " );
        }
    }
}

検証結果

項目	StringComparison.Ordinal の指定	時間
StartsWith	なし	0.96 秒
StartsWith	あり	0.09 秒
EndsWith	なし	3.69 秒
EndsWith	あり	0.04 秒

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