StringIO#each_line

static VALUE
strio_each(int argc, VALUE *argv, VALUE self)
{
    VALUE line;
    struct StringIO *ptr = readable(self);
    struct getline_arg arg;

    RETURN_ENUMERATOR(self, argc, argv);

    if (prepare_getline_args(ptr, &arg, argc, argv)->limit == 0) {
        rb_raise(rb_eArgError, "invalid limit: 0 for each_line");
    }

    while (!NIL_P(line = strio_getline(&arg, ptr))) {
        rb_yield(line);
    }
    return self;
}