为什么System.String.EndsWith（）有一个char重载而System.String.StartsWith（）没有？

Question

I was looking through System.String and I was wondering why the EndsWith and StartsWith methods aren't symmetric in terms of parameters they can take.

Specifically, why does System.String.EndsWith support a char parameter while System.String.StartsWith does not? Is this because of any limitation or design feature?

// System.String.EndsWith method signatures
[__DynamicallyInvokable]
public bool EndsWith(string value)

[ComVisible(false)]
[SecuritySafeCritical]
[__DynamicallyInvokable]
public bool EndsWith(string value, StringComparison comparisonType)

public bool EndsWith(string value, bool ignoreCase, CultureInfo culture)

[TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
internal bool EndsWith(char value)
{
  int length = this.Length;
  return length != 0 && (int) this[length - 1] == (int) value;
}

// System.String.StartsWith method signatures
[TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
[__DynamicallyInvokable]
public bool StartsWith(string value)

[SecuritySafeCritical]
[ComVisible(false)]
[__DynamicallyInvokable]
public bool StartsWith(string value, StringComparison comparisonType)

public bool StartsWith(string value, bool ignoreCase, CultureInfo culture)

Answer 1

Looking in ILSpy, this overload seems overwhelmingly to be called in IO code as

s.EndsWith(Path.DirectorySeparatorChar)

Presumably it's just something the C# team decided it would be useful to have to avoid repetitive code.

Note that it's much easier to make this check at the start ( s[0] == c vs s[s.Length - 1] == c ) which may also explain why they didn't bother to make a StartsWith overload.

Answer 2

This is an internal method that only is used in the following 8 methods in mscorlib :

• System.Security.Util.StringExpressionSet.CanonicalizePath(string path, bool needFullPath):string
• System.IO.IsolatedStorage.IsolatedStorageFile.DirectoryExists(string path):bool
• System.IO.Directory.GetDemandDir(string fullPath, bool thisDirOnly):string
• System.IO.DirectoryInfo.GetDirName(string fullPath):string
• System.Security.Util.URLString.IsRelativeFileUrl:bool
• System.IO.DirectoryInfo.MoveTo(string destDirName):void
• System.IO.DirectoryInfo.Parent:DirectoryInfo
• System.Globalization.CultureData.SENGDISPLAYNAME:string

Probably just for convenience and code reuse :)