Method: Enumerator.produce

Defined in:

enumerator.c

.produce(initial = nil) {|prev| ... } ⇒ Object

Creates an infinite enumerator from any block, just called over and over. The result of the previous iteration is passed to the next one. If initial is provided, it is passed to the first iteration, and becomes the first element of the enumerator; if it is not provided, the first iteration receives nil, and its result becomes the first element of the iterator.

Raising StopIteration from the block stops an iteration.

Enumerator.produce(1, &:succ)   # => enumerator of 1, 2, 3, 4, ....

Enumerator.produce { rand(10) } # => infinite random number sequence

ancestors = Enumerator.produce(node) { |prev| node = prev.parent or raise StopIteration }
enclosing_section = ancestors.find { |n| n.type == :section }

Using ::produce together with Enumerable methods like Enumerable#detect, Enumerable#slice_after, Enumerable#take_while can provide Enumerator-based alternatives for while and until cycles:

# Find next Tuesday
require "date"
Enumerator.produce(Date.today, &:succ).detect(&:tuesday?)

# Simple lexer:
require "strscan"
scanner = StringScanner.new("7+38/6")
PATTERN = %r{\d+|[-/+*]}
Enumerator.produce { scanner.scan(PATTERN) }.slice_after { scanner.eos? }.first
# => ["7", "+", "38", "/", "6"]

Yields:

• (prev)

# File 'enumerator.c', line 3077

static VALUE
enumerator_s_produce(int argc, VALUE *argv, VALUE klass)
{
    VALUE init, producer;

    if (!rb_block_given_p()) rb_raise(rb_eArgError, "no block given");

    if (rb_scan_args(argc, argv, "01", &init) == 0) {
        init = Qundef;
    }

    producer = producer_init(producer_allocate(rb_cEnumProducer), init, rb_block_proc());

    return rb_enumeratorize_with_size_kw(producer, sym_each, 0, 0, producer_size, RB_NO_KEYWORDS);
}