doc/LPC/foreach

NAME
        foreach

SYNTAX
        foreach (<var> : <expr>) <statement>;
        foreach (<var>, <var2>, ... ,<varN> : <expr>) <statement>;

        foreach (<var> : <expr1> .. <expr2>) <statement>;
        foreach (<var>, <var2>, ... ,<varN> : <expr1>..<expr2> ) <statement>;

        /* MudOS compatibility only - not for new code: */
        foreach (<var> in <expr>) <statement>;
        foreach (<var>, <var2>, ... ,<varN> in <expr>) <statement>;

DESCRIPTION
        The instruction evaluates its range specification - either a
        simple <expr> which can yield an array, a struct, a string, a
        mapping or an integer, or an integer range <expr1> through
        <expr2> - and executes <statement> once for each value in the
        range. The respective value is assigned to <var> right before
        <statement> is executed.

        A 'break' in the <statement> will terminate the loop. A
        'continue' will continue the execution from the beginning of
        the loop.

        Every <var> specification can declare a new local variable, whose
        scope is the whole foreach() statement.


        The normal form (one <expr>):

            <expr> is evaluated and has to yield an array, a struct, a
            string or a mapping (or reference to the former), or an
            integer.

            If <expr> is a array, struct, or string, the values of
            <expr> (in case of the string, the integer values of the
            characters) are then assigned one by one in order of
            occurence to <var>, and <statement> is executed for every
            assignment.

            If <expr> is a mapping, the keys are assigned one by one
            to <var>, and the values for each key are assigned in
            order to <var2>..<varN>.  If there are more values than
            variable, the extraneous values are ignored. Due to the
            nature of mappings, a specific order of the keys can not
            be guaranteed.

            If <expr> evaluates to a reference to an array, mapping, or
            string, the loop will assign references to the values into
            the variables. This allows the loop body to change the contents
            of the original data.

            If <expr> evaluates to an integer, the loop will count up <var>
            from 0 to <expr>-1, basically implementing a count loop.

            If <expr> evaluates to a coroutine, the loop will call the
            coroutine until the coroutine finishes execution. All values
            from the coroutine's yield() calls will be assigned to <var>,
            essentially using the coroutine as a generator function.

            If there are more variables than necessary, the unneeded ones
            are not changed.


        The ranged form (<expr1> .. <expr2>):

            <expr1> and <expr2> are evaluated and must yield integers.
            The loop will count up <var> from <expr1> to <expr2>, basically
            implementing a counted loop.

            If <expr1> is less than <expr2>, the loop will terminate at once.

            If there are more than variable, the unneeded ones are not
            changed.



        WHAT HAPPENS IF <expr> IS CHANGED IN THE LOOP?

        If <expr> yields an array or struct:
         - assignments to single elements or to array ranges effect
           the values assigned to the variable:
             a = ({1, 2, 3})
             foreach(x : a) { a[1..2] = ({4, 5}); write(x+" "); }
           will write ("1 4 5 ").
         - operations which implicitly copy the array or struct (this
           includes range assignments which change the size) don't
           have an effect on the loop.

        If <expr> yields a mapping, the loop will run over the indices
        the mapping had at the begin of the loop. Deleted indices are silently
        skipped, new indices ignored, but changes of the data of existing
        indices are acknowledged.

        If <expr> yields a string, the value used at the start of the loop
        remains.


WARNING
        The additional syntax forms using "in" as keyword are meant
        to make re-engineering of MudOS objects easier. Do not use them
        for newly written code, as they may not be available in future.


EXAMPLES
        // Call quit() in all interactive users
        foreach(o : users()) o->quit();
        foreach(object o : users()) o->quit();

        // Print the contents of a mapping <m>
        foreach(key, value : m) printf("%O:%O\n", key, value);
        foreach(mixed key, mixed value : m) printf("%O:%O\n", key, value);

        // Don't change the content of a string: s remains "FOOBAR".
        s = "FOOBAR";
        foreach(i : s) i += 32;

        // Do change the content of a string: s will become "foobar".
        s = "FOOBAR";
        foreach(i : &s) i += 32;

        // Count from 0 to 5
        foreach(i : 6) printf("%d\n", i);

        // Count from 1 to 6
        foreach(i : 1 .. 6) printf("%d\n", i);

HISTORY
        LDMud 3.3.44 introduced the use of references, the loop over
          an integer expression, and the loop over an integer range.
        LDMud 3.3.266 added support for structs.
        LPMud 3.6.5 added support for coroutines.


SEE ALSO
        for(LPC), yield(LPC)