Swift: print() vs println() vs NSLog()

转自 http://stackoverflow.com/questions/25951195/swift-print-vs-println-vs-nslog#

1. println vs print:

   Prior to Swift 2, println would add a newline at the end of the results, whereas print would not.

   Starting in Swift 2, println is no longer used. One would generally use print (either without appendNewline parameter, or having that parameter set to true) to print a line followed with a newline character. You would use print with appendNewline of false if you want to print a string without a newline at the end.

2. NSLog vs print/println:

   • NSLog is slower;

   • NSLog adds a timestamp and identifier to the output, whereas println will not;

   • NSLog synchronizes the log statements so that if you're issuing logs from different threads concurrently, they won't overlap with each other; println can result in jumbled output if performed simultaneously from separate threads without doing some synchronization (e.g. dispatching it to some serial queue, such as the main queue);

   • When performed on physical device, NSLog statements appear in the device's console whereas println only appears in the debugger console.

Generally in Swift, you'd use print/println, though you can use NSLog, when needed (e.g., it's critical that it appears in the console or if you're doing this from multiple threads and you don't want to have to synchronize this yourself). Either of these should be able to display your dictionary without incident.

you can pass in an NSString to println, but not NSLog; you can add args for NSLog, but not println; Swift style string interpolation sometimes crashes for NSLog, but not println.