instance method

Enumerator#size

() -> (::Integer | ::Float)?

e.size → int, Float::INFINITY or nil

static VALUE
enumerator_size(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);
    int argc = 0;
    const VALUE *argv = NULL;
    VALUE size;

    if (e->procs) {
        struct generator *g = generator_ptr(e->obj);
        VALUE receiver = rb_check_funcall(g->obj, id_size, 0, 0);
        long i = 0;

        for (i = 0; i < RARRAY_LEN(e->procs); i++) {
            VALUE proc = RARRAY_AREF(e->procs, i);
            struct proc_entry *entry = proc_entry_ptr(proc);
            lazyenum_size_func *size_fn = entry->fn->size;
            if (!size_fn) {
                return Qnil;
            }
            receiver = (*size_fn)(proc, receiver);
        }
        return receiver;
    }

    if (e->size_fn) {
        return (*e->size_fn)(e->obj, e->args, obj);
    }
    if (e->args) {
        argc = (int)RARRAY_LEN(e->args);
        argv = RARRAY_CONST_PTR(e->args);
    }
    size = rb_check_funcall_kw(e->size, id_call, argc, argv, e->kw_splat);
    if (!UNDEF_P(size)) return size;
    return e->size;
}

Returns the size of the enumerator, or nil if it can’t be calculated lazily.

Example

(1..100).to_a.permutation(4).size # => 94109400
loop.size # => Float::INFINITY
(1..100).drop_while.size # => nil

Note that enumerator size might be inaccurate, and should be rather treated as a hint. For example, there is no check that the size provided to ::new is accurate:

Example

e = Enumerator.new(5) { |y| 2.times { y << it} }
e.size # => 5
e.to_a.size # => 2

Another example is an enumerator created by ::produce without a size argument. Such enumerators return Infinity for size, but this is inaccurate if the passed block raises StopIteration:

Example

e = Enumerator.produce(1) { it + 1 }
e.size # => Infinity

e = Enumerator.produce(1) { it > 3 ? raise(StopIteration) : it + 1 }
e.size # => Infinity
e.to_a.size # => 4

See also #rewind #with_index #peek_values #with_object also in 4.1 · 3.4 · 3.3 · 3.2 · 3.1 · 3.0

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