Why do the overloads of String.Format exist?

I was using Reflector to look at the implementation of String.Format and had always been under the impression that the overloads of String.Format that took 1, 2 & 3 arguments were optimized versions of the method that takes an object array. However, what I found was that internally they create an object array and then call a method that takes an object array.

1 arg

public static string Format(string format, object arg0)
{
    if (format == null)
    {
        throw new ArgumentNullException("format");
    }
    return Format(null, format, new object[] { arg0 });
}

2 args

public static string Format(string format, object arg0, object arg1)
{
    if (format == null)
    {
        throw new ArgumentNullException("format");
    }
    return Format(null, format, new object[] { arg0, arg1 });
}

3 args

public static string Format(string format, object arg0, object arg1, object arg2)
{
    if (format == null)
    {
        throw new ArgumentNullException("format");
    }
    return Format(null, format, new object[] { arg0, arg1, arg2 });
}

Object array

publ开发者_高级运维ic static string Format(string format, params object[] args)
{
    if ((format == null) || (args == null))
    {
        throw new ArgumentNullException((format == null) ? "format" : "args");
    }
    return Format(null, format, args);
}

Internally they all end up using the same code and so using the 1, 2 & 3 argument versions are no faster than the object array version.

So my question is - why do they exist?

When you use the object array version with a comma separated list of values, the compiler automatically converts the arguments into an object array because of the params/ParamArray keyword which is essentially what the 1, 2 & 3 versions do, so they seem redundant. Why did the BCL designers add these overloads?

One reason, as Hans mentions, is that creating an array is a lot of unnecessary overhead in most common cases of formatting a string. This saves space in the EXE.

Another reason is that not all languages support variadic functions (use of params in C#). This allows users of those languages to avoid array creation for the most common cases of string formatting. This saves a lot for languages that don't have simple syntax for array creation and initialization.

You are forgetting about the code in the app required to make the call. Creating the array and filling it takes a lot more IL than just passing 3 args.