Loops - foreach

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A foreach loop is a control structure for repeating a block of code a number of times. It will run as long as there are more elements in the collection.

The definition has 5 parts:

keyword foreach
initialization enclosed in parentheses:
- declaration of the loop variable
- keyword in
- collection to iterate
1 or more statements enclosed in curly brackets

String[] mTwain;
mTwain.pushBack("The secret");
mTwain.pushBack("of");
mTwain.pushBack("getting ahead");
mTwain.pushBack("is");
mTwain.pushBack("getting started");

foreach (String s in mTwain) {
  print(s + " ");
}

Initialization

The statement in the parenthesis initializes the iterator variable for the loop. The iterator must be declared as the same type as the collection. For example, if your array is of type String, then the iterator must be a string as well.

You can loop through any type of collection with foreach, even your own structs.

Usage

You should use a foreach loop when you would use a for loop with the following pattern:

for (Integer i = 0; i < array.length(); i++) {
 print(array[i]);
}

This is a more compact structure that and handles the indexing for you. It is also faster!

Note

The foreach statement is used to iterate through the array to get the information that you want, but can not be used to add or remove items from the source array to avoid unpredictable side effects.
Arrays of intrinsic types, such as String or Integer, are passed by value, while an array or a struct is passed by reference. Therefore, while inside a foreach loop, you can update a struct property, but not a String value.