Milestone 1

for statement

The for statement supports iteration.

Usage

The general form of the for statement is

for ( /* variable declaration and expression */ ) {
    /* for block */
} else {
    /* code executed if iteration doesn't exit early */
}
/* code after for statement */

The else clause is optional.

Description

Execution

A for statement works with Iterables. Before the for block an iteration variable (assignable to Iterator<T>, for some T) is declared, and an Iterable-typed expression is given. The for block is executed with the declared variable taking the value of successive items returned from the Iterator obtained from the Iterable. Execution proceeds until the Iterator is exhausted or an 'early exit' occurs.

break and continue

Within the for block the break directive can be used to exit the block early without iterating over the remaining items in the Iterator. This is one form of 'early exit'.

The continue directive can be used to skip execution of the remainder of the block and proceed with the next item from the Iterator.

Early Exit

If the for block ends with a return, break, or throw directive the iteration is said to have exited early. In the return and throw cases control is returned directly to the caller; in the break case execution proceeds with the code following the else clause. Therefore, in all cases of early exit the else block is not executed.

The else clause is ideally suited to situations where the for statement is being used to find something in a sequence or list, and the sought item has not been found:

variable Boolean minors;
for (p in people) {
    if (p.age<18) {
        minors = true;
        break;
    }
}
else {
    minors = false;
}

Unsupported features

Ceylon not support the C-style for statement, with an initialising statement, iteration statement and termination condition. This isn't a problem in practice; see what the Tour has to say.

See also