In swift 2.0, print()
automatically adds a newline character. In swift 1.2, println()
and print()
used to be separate functions. So how do I print some text and not add a newline to it since swift no longer has a print function that does not append newlines.
print without newline in swift
91.5k views Asked by Ankit Goel AtThere are 5 answers
print
function has changed completely since the late revision of Swift, now it looks much simpler and there are variant of method to print to standard console.
The method signature for print looks something like this,
public func print<Target>(_ items: Any..., separator: String = default, terminator: String = default, to output: inout Target) where Target : TextOutputStream
And here are some usecases,
print("Swift is awesome.")
print("Swift", "is", "awesome", separator:" ")
print("Swift", "is", "awesome", separator:" ", terminator:".")
Prints:
Swift is awesome.
Swift is awesome
Swift is awesome.
Concatenating
print("This is wild", terminator: " ")
print("world")
Prints:
This is wild world
So, using terminator, you should be careful that the contents are relevant to same line.
Printing Object with CustomStringConvertible
struct Address {
let city: String
}
class Person {
let name = "Jack"
let addresses = [
Address(city: "Helsinki"),
Address(city: "Tampere")
]
}
extension Person: CustomStringConvertible {
var description: String {
let objectAddress = unsafeBitCast(self, to: Int.self)
return String(format: "<name: \(name) %p>", objectAddress)
}
}
let jack = Person()
print(jack)
Prints:
<name: Jack 0x608000041c20>
CustomDebugStringConvertible
extension Person: CustomDebugStringConvertible {
var debugDescription: String {
let objectAddress = unsafeBitCast(self, to: Int.self)
let addressString = addresses.map { $0.city }.joined(separator: ",")
return String(format: "<name: \(name), addresses: \(addressString) %p>",objectAddress)
}
}
Now, with lldb, you can use po command and it will print object as this in lldb console,
<name: Jack, addresses: Helsinki,Tampere 0x60c000044860>
Logging to file using TextOutputStream
struct MyStreamer: TextOutputStream {
lazy var fileHandle: FileHandle? = {
let fileHandle = FileHandle(forWritingAtPath: self.logPath)
return fileHandle
}()
var logPath: String = "My file path"
mutating func write(_ string: String) {
fileHandle?.seekToEndOfFile()
fileHandle?.write(string.data(using:.utf8)!)
}
}
Now, using print to stream,
print("First of all", to: &myStream )
print("Then after", to: &myStream)
print("And, finally", to: &myStream)
Prints to file:
First of all
Then after
And finally
CustomReflectable
extension Person: CustomReflectable {
var customMirror: Mirror {
return Mirror(self, children: ["name": name, "address1": addresses[0], "address2": addresses[1]])
}
}
Now, in lldb debugger, if you use command po,
> po person
Result would be something like this,
▿ <name: Jack, addresses: Tampere Helsinki 0x7feb82f26e80>
- name : "Jack"
▿ address1 : Address
- city : "Helsinki"
▿ address2 : Address
- city : "Tampere"
let description = String(describing: yourVariable)
The description
variable here would hold exactly the same output you would get in console by using print()
function.
So you can replace anything in the output.
For example I use this code to print JSON in single line:
print(description.replacingOccurrences(of: "\n", with: " "))
In Swift 2.0 you can do this:
Basic version
print("Hello World")
result "Hello World\n"
Using terminator
print("Hello World", terminator:"")
result "Hello World"
Using separator
print("Hello", "World", separator:" ")
result "Hello World\n"
Using separator and terminator
print("Hello", "World", separator:" ", terminator:"")
result "Hello World"
Using one variable
var helloworld = "Hello World"
print(helloworld)
result "Hello World\n"
Using two variables
var hello = "Hello"
var world = "World"
print (hello, world)
result "Hello World\n"
Starting in Swift 2.0, the recommended method of printing without newline is: