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 ReplaceFir         


        

Answer 1

It is better to use String.Concat than String.Format if you know that format is not change data, and just concatenation is desired.

Answer 2

Mine is

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

Answer 3

This is a little extension method using latest syntax and correct validations

public static class StringExtensions
{
    public static string FirstCharToLower(this string input)
    {
        switch (input)
        {
            case null: throw new ArgumentNullException(nameof(input));
            case "": throw new ArgumentException($"{nameof(input)} cannot be empty", nameof(input));
            default: return input.First().ToString().ToLower() + input.Substring(1);
        }
    }
}

Answer 4

I like the accepted answer, but beside checking string.IsNullOrEmpty I would also check if Char.IsLower(name[1]) in case you are dealing with abbreviation. E.g. you would not want "AIDS" to become "aIDS".

Answer 5

If you don't want to reference your string twice in your expression you could do this using System.Linq.

new string("Hello World".Select((c, i) => i == 0 ? char.ToLower(c) : c).ToArray())

That way if your string comes from a function, you don't have to store the result of that function.

new string(Console.ReadLine().Select((c, i) => i == 0 ? char.ToLower(c) : c).ToArray())

Answer 6

Combined a few and made it a chainable extension. Added short-circuit on whitespace and non-letter.

public static string FirstLower(this string input) => 
    (!string.IsNullOrWhiteSpace(input) && input.Length > 0 
        && char.IsLetter(input[0]) && !char.IsLower(input[0]))
    ? input[0].ToString().ToLowerInvariant() + input.Remove(0, 1) : input;