String - append char

[Matesax]

Hi,
I need to append chars into string in foreach statement.void main(string[] args)
{
        string

                result = "",
                source = chomp(readText(args[1]));

        foreach(int index, char letter; source)
                result += letter; //14

        writeln(result);
}

But it returning:

main.d:14: Error: 'result' is not a scalar, it is a string
main.d:14: Error: incompatible types for ((result) += (letter)): 
'string' and 'char'
I try an pointer, but it damaged a string...
Thank you for help.