react native - Checking for nil parameter and if that parameter is an empty string in Swift -

there may or may not easier way write this, feel being novice @ swift, missing something. have parameter (filename) method optional string? need check if nil, or if empty string. code have, , works fine, seems bit more concise/readable.

func writefile(filename: string?, withcontents contents: string, errorcallback failurecallback: rctresponsesenderblock, callback successcallback: rctresponsesenderblock) -> void {    // if filename has value -- not nil   if let filename = filename {     // check see if string isn't empty     if count(filename) < 1 {       // craft failure message       let resultsdict = [         "success": false,         "errmsg": "filename empty"       ]        // execute javascript failure callback handler       failurecallback([resultsdict])        return; // halt execution of function     }     // else, filename nil, , should return same error message.   } else {     // craft failure message     let resultsdict = [       "success": false,       "errmsg": "filename empty"     ]      // execute javascript failure callback handler     failurecallback([resultsdict])      return; // halt execution of function   } } 

how

first create nil string optional set example var filename: string?

now code lets see if filename nil/empty in 1 simple line:

if (filename ?? "").isempty {   println("empty") } else {   println("not empty") } 

this uses ??, swift "nil coalescing operator". (link)

for expression:

a ?? b 

where a optional says:

if not nil, return a. if nil, return b instead.

so

if (filename ?? "").isempty 

says

first, evaluate filename , see if it's nil. if so, replace empty string.

next, check result see if it's empty.