Question

In C# you can implicitly concatenate a string and let’s say, an integer:

string sth = "something" + 0;

My questions are:

1. Why, by assuming the fact that you can implicitly concatenate a string and an int, C# disallows initializing strings like this:

   string sth = 0; // Error: Cannot convert source type 'int' to target type 'string'
   

2. How C# casts 0 as string. Is it 0.ToString() or (string)0 or something else?

3. How to find an answer of the previous question?

Answer 1

It compiles to a call to String.Concat(object, object), like this:

string sth = String.Concat("something", 0);

(Note that this particular line will actually be optimized away by the compiler)

This method is defined as follows: (Taken from the .Net Reference Source)

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

        if (arg1==null) { 
            arg1 = String.Empty;
        } 
        return Concat(arg0.ToString(), arg1.ToString());
    }

(This calls String.Concat(string, string))

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To discover this, you can use ildasm, or Reflector (in IL or in C# with no optimizations) to see what the + line compiles to.