BestPractice - Transform first character of a string into lower case

Question

I'd like to have a method that transforms the first character of a string into lower case.

My approaches:

1.

public static string ReplaceFirstCharacterToLowerVariant(string name)
{
    return String.Format("{0}{1}", name.First().ToString().ToLowerInvariant(), name.Substring(1));
}

2.

public static IEnumerable<char> FirstLetterToLowerCase(string value)
{
    var firstChar = (byte)value.First();
    return string.Format("{0}{1}", (char)(firstChar + 32), value.Substring(1));
}

What would be your approach?

Answer 1

I would use this:

Char.ToLowerInvariant(name[0]) + name.Substring(1)

Your first solution is not optimized: string.Format is slow and you don't need it if you have a format that will never change.

The second is ugly and not maintainable.

Answer 2

Mine is

if (!string.IsNullOrEmpty (val) && val.Lenght >0)
{
    return val[0].ToString().ToLowerInvariant() + val.Remove (0,1);   
}

Answer 3

Depending on the situation, a little defensive programming might be desirable:

public static string FirstCharacterToLower(string str)
{
    if (String.IsNullOrEmpty(str) || Char.IsLower(str, 0))
        return str;

    return Char.ToLowerInvariant(str[0]).ToString() + str.Substring(1);
}

The if statement also prevents a new string from being built if it's not going to be changed anyway. You might want to have the method fail on null input instead, and throw an ArgumentNullException.

As people have mentioned, using String.Format for this is overkill.