Formatting
Type-safe, functional string formatting in Swift.
Inspired by Chris Done's excellent Haskell library.
import Formatting
format("Hello, " % string % "!", "world")
// "Hello, world!"Introduction
Traditional string formatting methods (interpolation, printf, and template strings) can lead to subtle (and not so subtle) runtime bugs.
print("Hello, \(thing)!") // Hello, nil!
print("Hello, \(thing)!") // Hello, Optional("world")!NSLog(@"Hello, %@!", thing); // Hello, (null)!Formatting brings compile-time checks.
print("Hello, " % string % "!", thing) // Value of optional type String? not unwrappedAnd composability.
let greet =
format("Hello, " % string % "!")
greet("world") // Hello, world!Composing formatters
Use % to build a formatter with strings and other formatters.
format(string % " is " % int % "years old.", "Alice", 25)
// "Alice is 25 years old."Use <> to pass the previous formatter argument to the next formatter.
format(yyyy % "-" <> MM % "-" <> dd, Date())
// "2016-06-28"Use .% to feed the result of one formatter into another.
format(left(2, "0") .% hex, 10)
// "0a"Call format without arguments to return a curried formatter function.
let log =
format(right(5) % " -- [" % iso8601 % "] " % string)
let infoLog = log("INFO")
let debugLog = log("DEBUG")
infoLog(Date())("Logging in...")
// "INFO -- [2016-06-28T12:34:56Z] Logging in..."
debugLog(Date())("Logged in successfully!")
// "DEBUG -- [2016-06-28T12:34:56Z] Logged in successfully!"License
Formatting is available under the MIT license. See the LICENSE file for more information.