Why are the instance variables listed in validation for subclasses of built-in classes?

Question

Why is there a change in validation behavior when I subclass an inline class. But it is not visible when I subclass custom.

class MainError end class AnotherTestError < StandardError def initialize @label_test = "hey!" end end class TestError < MainError def initialize @label_test = "hey!" end end a = AnotherTestError.new puts a.inspect # output: #<AnotherTestError: AnotherTestError> t = TestError.new puts t.inspect # output: #<TestError:0x007f99e12409f0 @label_test="hey!"> 

Answer 1

Since many (most? All?) Inline classes

• written in C and
• have #inspect overriden.

For example, an Exception (superclass StandardError ) defines #inspect as follows:

 exc_inspect(VALUE exc) { VALUE str, klass; klass = CLASS_OF(exc); exc = rb_obj_as_string(exc); if (RSTRING_LEN(exc) == 0) { return rb_str_dup(rb_class_name(klass)); } str = rb_str_buf_new2("#<"); klass = rb_class_name(klass); rb_str_buf_append(str, klass); rb_str_buf_cat(str, ": ", 2); rb_str_buf_append(str, exc); rb_str_buf_cat(str, ">", 1); return str; } 

The interesting part is building the return string.

---

Object#inspect , on the other hand, defines:

 static VALUE rb_obj_inspect(VALUE obj) { if (rb_ivar_count(obj) > 0) { VALUE str; VALUE c = rb_class_name(CLASS_OF(obj)); str = rb_sprintf("-<%"PRIsVALUE":%p", c, (void*)obj); return rb_exec_recursive(inspect_obj, obj, str); } else { return rb_any_to_s(obj); } } 

which recursively includes instance variables with name and value.