// closures.groovy — closures: blocks of code you can store, pass and call.

// A closure literal: { parameters -> body }
def greet = { String name -> "Hello, $name!" }
println greet('Acme')                    // call like a method
println greet.call('Globex')             // or with call()

// One parameter? Use the implicit 'it'
def shout = { it.toUpperCase() + '!' }
println shout('boomi')

// No parameters
def now = { -> 'it is time' }
println now()

// Multiple parameters and default values
def lineTotal = { qty, price, discount = 0 -> qty * price * (1 - discount / 100) }
println lineTotal(10, 20)                // 200
println lineTotal(10, 20, 15)            // 170.00

// Closures as arguments: the last closure can go outside the parentheses
def retry(int times, Closure action) {
    for (attempt in 1..times) {
        try {
            return action(attempt)
        } catch (e) {
            println "  attempt $attempt failed: ${e.message}"
        }
    }
    'gave up'
}
def result = retry(3) { attempt ->
    if (attempt < 3) throw new RuntimeException('timeout')
    "succeeded on attempt $attempt"
}
println result

// Closures capture variables from where they were defined — and CAN change them
def total = 0
[250, 90, 1200].each { amount -> total += amount }
println "Total: $total"                  // 1540

// Returning closures: a function factory
def multiplier = { factor -> { number -> number * factor } }
def triple = multiplier(3)
println triple(7)                        // 21

// Method pointer: turn a method into a closure with .&
def upper = 'x'.&toUpperCase             // bound to the string 'x'
println upper()                          // X
def isEven = { it % 2 == 0 }
println([1, 2, 3, 4].findAll(isEven))    // [2, 4]