Reason 11 overloads string.Concat

Question

I just noticed that there are 11 method overloads string.Concat()

public static string Concat(IEnumerable<string> values);
public static string Concat<T>(IEnumerable<T> values);
public static string Concat(object arg0);
public static string Concat(params object[] args);
public static string Concat(params string[] values);
public static string Concat(object arg0, object arg1);
public static string Concat(string str0, string str1);
public static string Concat(object arg0, object arg1, object arg2);
public static string Concat(string str0, string str1, string str2);
public static string Concat(object arg0, object arg1, object arg2, object arg3);
public static string Concat(string str0, string str1, string str2, string str3);

What is the reason for this? Both

public static string Concat(params object[] args);
public static string Concat<T>(IEnumerable<T> values);

should be the only necessary because they are just as comfortable / powerful. MSDN does not give an answer to this, and if you remove 9 “duplicate” overloads from the framework, no one will notice.

Answer 1

The primary motivation for solving this implementation is performance.

As you rightly noted, there can only be two:

public static string Concat(params object[] args);
public static string Concat<T>(IEnumerable<T> values);

# "params enumerable", IEnumerable<T> T[] - . .

, .

string x = Foo();
string y = Bar();
string z = x + y;

? ToString codegen'd

string x = Foo();
string y = Bar();
object[] array = new string[2];
array[0] = x;
array[1] = y;
string z = string.Concat(array);

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static string Concat(string, string)

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string x = Foo();
string y = Bar();
string z = string.Concat(x, y);

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https://ericlippert.com/2013/06/17/string-concatenation-behind-the-scenes-part-one/

Answer 2

(IEnumerable<String>) (IEnumerable<T>) .

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• IEnumerable<T> - Object[] ).

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