`foreach` Loop

The foreach loop iterates over the elements of an array, the characters of a string, or the values of an object.

foreach variable in expression do
    # body
end

The do keyword is required. The block is closed with end.

Iterating over arrays

foreach item in Data.items do
    item.processed = true
end

Iterating over strings

When the source is a string, each iteration yields a single-character string:

foreach ch in "hello" do
    # ch is "h", "e", "l", "l", "o"
end

Iterating over objects

When the source is an object, foreach iterates over the object’s values:

foreach val in Data.scores do
    total += val
end

To iterate over an object’s keys, use Keys():

foreach key in Keys(Data.scores) do
    var value = Data.scores[key]
end

Non-iterable values

Only arrays, strings, and objects are iterable. Attempting to iterate over a number, boolean, or null is an error:

Compile-time - if the collection expression is a literal of a non-iterable type (e.g. foreach x in 42 do), the compiler reports error JM3402.
Runtime - if a variable evaluates to a non-iterable type at runtime, error JM5402 is raised.

Loop variable scoping

The iteration variable is scoped to the loop body and does not exist outside the loop.

Collection modification

Modifying the collection being iterated causes a runtime error. Use a separate collection for additions:

# INCORRECT - runtime error
foreach item in Data.items do
    Data.items = Append(Data.items, item)
end

# CORRECT - collect into a separate array
var additions = []
foreach item in Data.items do
    if item.shouldDuplicate then
        additions = Append(additions, item)
    end
end
foreach addition in additions do
    Data.items = Append(Data.items, addition)
end

foreach Loop