swift - stringByAppendingString doesn't return modified string -

this trying in playground file. result want second println result using stringbyappendingstring. isn't stringbyappendingstring supposed return modified string? doing wrong here?

var reportsummary:string = "total: \t\t300.00" reportsummary.stringbyappendingstring("net: \t\t200.00") println(reportsummary) // total:    300.00   var reportsum = "total: \t300.00\n" var netsum = "net: \t\t200.00\n" var sum = reportsum + netsum println(sum) // total:    300.00 // net:      200.00 

the stringbyappendingstring message creates , returns new string. doesn't modify receiver (the original string).

if want use combined string, need return value. code posted ignores return value. can, example, store returned string in reportsummary variable this:

var reportsummary:string = "total: \t\t300.00" reportsummary = reportsummary.stringbyappendingstring("\nnnet: \t\t200.00") println(reportsummary) 

you might use += operator, though:

var reportsummary = "total: \t\t300.00" reportsummary += "\nnet: \t\t200.00" println(reportsummary) 

or can use extend method:

var reportsummary = "total: \t\t300.00" reportsummary.extend("\nnet: \t\t200.00") println(reportsummary) 

or can explicitly use foundation type nsmutablestring:

let reportsummary: nsmutablestring = "total: \t\t300.00" reportsummary.appendstring("\nnet: \t\t200.00") println(reportsummary)