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.