Enumerator::Lazy.new

Lazy.new(obj, size=nil) { |yielder, *values| block }

static VALUE
lazy_initialize(int argc, VALUE *argv, VALUE self)
{
    VALUE obj, size = Qnil;
    VALUE generator;

    rb_check_arity(argc, 1, 2);
    if (!rb_block_given_p()) {
        rb_raise(rb_eArgError, "tried to call lazy new without a block");
    }
    obj = argv[0];
    if (argc > 1) {
        size = argv[1];
    }
    generator = generator_allocate(rb_cGenerator);
    rb_block_call(generator, id_initialize, 0, 0, lazy_init_block_i, obj);
    enumerator_init(self, generator, sym_each, 0, 0, 0, size, 0);
    rb_ivar_set(self, id_receiver, obj);

    return self;
}

Creates a new Lazy enumerator. When the enumerator is actually enumerated (e.g. by calling force), obj will be enumerated and each value passed to the given block. The block can yield values back using yielder. For example, to create a “filter+map” enumerator:

Example

def filter_map(sequence)
  Lazy.new(sequence) do |yielder, *values|
    result = yield *values
    yielder << result if result
  end
end

filter_map(1..Float::INFINITY) {|i| i*i if i.even?}.first(5)
#=> [4, 16, 36, 64, 100]

See also #chunk #chunk_while also in 4.1 · 4.0 · 3.4 · 3.2 · 3.1 · 3.0

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