Can you break from a Groovy each closure

Question

Is it possible to break from a Groovy  each Closure   or should I be using a classic loop instead

User · Answer

You can t break from a Groovy each loop  but you can break from a java  quot enhanced quot  for loop  def a    1  2  3  4  5  6  7   for  def i   a        if  i  lt  2          continue     if  i  gt  5          break     println i    Output  2 3 4 5  This might not fit for absolutely every situation but it s helped for me

User · Answer

1  10  each   if  it  lt  5   println it  else  return false

User · Answer

I agree with other answers not to use an exception to break an each  I also do not prefer to create an extra closure eachWithBreak  instead of this I prefer a modern approach  let s use the each to iterate over the collection  as requested  but refine the collection to contain only those elements to be iterated  for example with findAll  collection findAll    endCondition   each   doSomething      For example  if we what to break when the counter    3 we can write this code  already suggested    0  5       findAll   it  lt  3         each   println it    This will output 0 1 2  So far so good  but you will notice a small discrepancy though  Our end condition  negation of counter    3 is not quite correct because   counter  3  is not equivalent with it  lt  3  This is necessary to make the code work since findAll does not actually break the loop but continues until the end  To emulate a real situation  let s say we have this code  for  n in 0  5        if  n    3          break     println n    but we want to use each  so let s rewrite it using a function to simulate a break condition  def breakWhen nr    nr    3    0  5       findAll    breakWhen it         each   println it    with the output  0 1 2 4 5  now you see the problem with findAll  This does not stop  but ignores that element where the condition is not met  To solve this issues  we need an extra variable to remember when the breaking condition become true  After this moment  findAll must ignore all remaining elements  This is how it should look like  def breakWhen nr    nr    3   def loop   true  0  5       findAll           if  breakWhen it               loop   false          breakWhen it   amp  amp  loop        each           println it        with the output  0 1 2  That s what we want

User · Answer

You could break by RETURN  For example     def a    1  2  3  4  5  6  7    def ret   0   a each  def n - gt      if  n  gt  5          ret   n       return ret             It works for me

User · Answer

Replace each loop with any closure   def list    1  2  3  4  5  list any   element - gt      if  element    2          return    continue      println element      if  element    3          return true    break     Output  1 3

User · Answer

Nope  you can t abort an  each  without throwing an exception   You likely want a classic loop if you want the break to abort under a particular condition   Alternatively  you could use a  find  closure instead of an each and return true when you would have done a break   This example will abort before processing the whole list   def a    1  2  3  4  5  6  7   a find        if  it  gt  5  return true    break     println it     do the stuff that you wanted to before break     return false    keep looping     Prints   1 2 3 4 5   but doesn t print 6 or 7   It s also really easy to write your own iterator methods with custom break behavior that accept closures   List metaClass eachUntilGreaterThanFive     closure - gt      for   value in delegate             if   value   gt  5   break         closure value           def a    1  2  3  4  5  6  7   a eachUntilGreaterThanFive       println it     Also prints   1 2 3 4 5

User · Answer

Just using special Closure     declare and implement  def eachWithBreak     list  Closure c - gt    boolean bBreak   false   list each     it - gt       if  bBreak  return      bBreak   c it         def list    1 2 3 4 5 6  eachWithBreak list    it - gt    if  it  gt  3  return true    break  eachWithBreak    println it   return false    next it

User · Answer

No  you can t break from a closure in Groovy without throwing an exception  Also  you shouldn t use exceptions for control flow   If you find yourself wanting to break out of a closure you should probably first think about why you want to do this and not how to do it  The first thing to consider could be the substitution of the closure in question with one of Groovy s  conceptual  higher order functions  The following example   for   i in 1  10    if  i  lt  5  println i  else return    becomes   1  10  each if  it  lt  5  println it    becomes   1  10  findAll it  lt  5  each println it     which also helps clarity  It states the intent of your code much better   The potential drawback in the shown examples is that iteration only stops early in the first example  If you have performance considerations you might want to stop it right then and there   However  for most use cases that involve iterations you can usually resort to one of Groovy s find  grep  collect  inject  etc  methods  They usually take some  configuration  and then  know  how to do the iteration for you  so that you can actually avoid imperative looping wherever possible

[groovy] Can you break from a Groovy "each" closure?

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