带有 optional 参数的 Groovy 闭包

Question

我想定义一个接受一个参数的闭包(我用 it 指代)
有时我想向闭包传递另一个额外的参数。
我怎样才能做到这一点？

Answer 1

您可以将第二个参数设置为默认值(例如 null):

def cl = { a, b=null ->
  if( b != null ) {
    print "Passed $b then "
  }
  println "Called with $a"
}

cl( 'Tim' )          // prints 'Called with Tim'
cl( 'Tim', 'Yates' ) // prints 'Passed Yates then Called with Tim

另一种选择是制作 b像这样的可变参数列表:

def cl = { a, ...b ->
  if( b ) {
    print "Passed $b then "
  }
  println "Called with $a"
}

cl( 'Tim' )                    // prints 'Called with Tim'
cl( 'Tim', 'Yates' )           // prints 'Passed [Yates] then Called with Tim
cl( 'Tim', 'Yates', 'Groovy' ) // prints 'Passed [Yates, Groovy] then Called with Tim