ForEach() : Why can't use break/continue inside

Question

Since ForEach() method loop through all a list members, Why cant use a break/continue clause while i can use them inside a normal foreach loop

lstTemp.ForEach(i=>
 {
   if (i == 3)
   break;
   //do sth
 }
);

Error:

"No enclosing loop out of which to break or continue"

Solution 1

Because ForEach is a method and not a regular foreach loop. The ForEach method is there for simple tasks, if you need to break or continue just iterate over lstTemp with a regular foreach loop.

Usually, ForEach is implemented like this:

public static ForEach<T>(this IEnumerable<T> input, Action<T> action)
{
  foreach(var i in input)
    action(i);
}

As it is a normal method call, action doesn't know anything about the enclosing foreach, thus you can't break.

Solution 2

return will act as continue in ForEach.

Example:

var list = new List<int>() {1, 2, 3, 4};
list.ForEach(i => 
    {
        if (i == 3)
            return;
        Console.WriteLine(i);
    }
);

Prints 1, 2, 4.

3 - skipped.

Solution 3

Presumably because you're using a lambda and the contents of the lambda are ignorant to the fact that it's being used inside a loop.

Solution 4

rather than using a break, perform a filter first like this (it may not be the exact filter you need, but illustrates the point)

lstTemp.Where(i => i!= 3).ForEach(i=> // do sth);

Solution 5

To iterate only part of the items and emulate the break perfectly, you can use FirstOrDefault:

lstTemp.FirstOrDefault(i=>
 {
   if (i == 3)
       return true;

   //do stuff

   return false;
 }
);

For list with 100000 items, if the 10th item is 3 it will iterate only 10 times, using the Where solution will work, but iterate the whole list first.

View more solutions

Comments

[Tesserex]

A well written ForEach extension should allow you to return false if you want it to break. But I can't say for sure since I don't know where you got your foreach. If you wrote it yourself that may be a good option.

[Juliet]

Looks like you want the TakeWhile function msdn.microsoft.com/en-us/library/bb534804%28v=VS.90%29.aspx

[CS Smit]

I found a better answer here: stackoverflow.com/questions/3145563/list-foreach-break

[Sergio]

-1 Not the samething. your code will run for every i != 3. The code presented will run until i == 3.

[James Gregory]

The Where method does not iterate the collection, see: deferred execution.

[Shadow The Kid Wizard]

@James maybe iterate isn't the right word.. but to find all matching items, somewhere somehow all items must be checked, isn't it?

[James Gregory]

Have a read of how the yield keyword works, because that's how LINQ queries operate. It's too long to explain here, but no, not all the items must be checked; only as many items as are requested by the call-chain will be checked. Exactly the same as your FirstOrDefault, which will iterate until it hits a match.

[Nigiri]

This seems the best way for 'continue'. Besides we can just write 'return' for 'break'.

[Lance]

Given that it's a method call, can I just return instead of break?

[Femaref]

No, you will just return from the method itself. You will not be able to break out of an outer foreach that way.

[Rafael]

this doesn't exactly answer the question. OP is asking why he/she can't use break/continue like a normal loop.

[code4life]

Try removing the do-while and use the break, LOL.