Why String.Concat returns 'True' instead of 'true' (the same with false)?

Question

I'm studying boxing and unboxing topic from C# 5.0 in a Nutshell by Joseph Albahari and Ben Albahari. Copyright 2012 Joseph Albahari and Ben Albahari, 978-1-449-32010-2, but I need to extend the deep of knowledge and I found the MSDN article: Boxing and Unboxing (C# Programming Guide), on it I found this example code (evidently not intrinsically related to the main topic):

Console.WriteLine (String.Concat("Answer", 42, true));

Once executed it returns:

Answer42True

Why this is happening with the literal 'true' (the same occurs with 'false')?

Execution test.

Thanks in advance.

@SonerGönül not sure that's the same question... It might be the *next* question. — Ant P, Mar 01 '14 at 17:42
@AntP This is exactly same question. Since `String.Concat` converts them to string, the real point will be why `true.ToString()` is `True` not `true`. — Soner Gönül, Mar 01 '14 at 17:43
No, it's not the same question, because the asker doesn't necessarily *know* that String.Concat converts its parameters to a string. So the answer to this question is "because String.Concat converts its parameters to a string and you're passing it a bool." Hence the *next* question might be as linked. You're jumping the gun. — Ant P, Mar 01 '14 at 17:45
The other question is most abstract, it serves as base to explain many of the facts (behavior of the String.ToString method, for example) of the mine. So, for my point of view, they aren't (precisely) the same. — InfZero, Mar 01 '14 at 17:50

score 5 · Answer 1 · answered Mar 01 '14 at 17:32

5

This is because....

true.ToString() == "True"

And String.Concat must convert its arguments to strings, while true is a bool!

answered Mar 01 '14 at 17:32

Ant P

24,820
5
68
105

BRAHIM Kamel · Accepted Answer · 2014-03-01T18:22:17.163

For the sample reason if you try to decompile String.Concat() method in mscorlib.dll you will get something like this

      for (int index = 0; index < args.Length; ++index)
      {
        object obj = args[index];
        values[index] = obj == null ? string.Empty : obj.ToString(); //which  will call the `ToString()` of `boolean struct` 

      }

ToString() method which is called by default by string.Concat method it is like this

 public override string ToString()
    {
      return !this ? "False" : "True";
    }

score 3 · Answer 3 · edited May 23 '17 at 11:57

Takea look at first of all: Why does Boolean.ToString output "True" and not "true"

There is no String.Concat(string, int, bool) overload, that's why your code calls nearest overload which is String.Concat(object, object, object).

And String.Concat(Object arg0, Object arg1, Object arg2) method implemented like this;

public static String Concat(Object arg0, Object arg1, Object arg2)
{
        if (arg0 == null)
        {
            arg0 = String.Empty;
        }

        if (arg1==null) {
            arg1 = String.Empty;
        }

        if (arg2==null) {
            arg2 = String.Empty;
        }

        return Concat(arg0.ToString(), arg1.ToString(), arg2.ToString());
}

As you can see, all objects convert to string at the last line.

That's why your code works like this;

String.Concat("Answer", 42.ToString(), true.ToString()));

And it will be;

String.Concat("Answer", "42", "True"));

And result will be;

Answer42True

score 2 · Answer 4 · answered Mar 01 '14 at 17:32

2

true is not a string. The framework must convert true or false into strings before concatenating them to the string, and it just so happens that the way that conversion is defined for them is that the first letter is capitalized.

answered Mar 01 '14 at 17:32

OSborn

895
4
10

Why String.Concat returns 'True' instead of 'true' (the same with false)?

4 Answers4