each_line

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

    RETURN_ENUMERATOR(self, argc, argv);

    if (argc > 0 && !NIL_P(argv[argc-1]) && NIL_P(rb_check_string_type(argv[argc-1])) &&
        NUM2LONG(argv[argc-1]) == 0) {
        rb_raise(rb_eArgError, "invalid limit: 0 for each_line");
    }

    while (!NIL_P(line = strio_getline(argc, argv, readable(ptr)))) {
        rb_yield(line);
    }
    return self;
}