class Thread

def inheritable_thread_local_var_get(...) 

def inheritable_thread_local_var_get(...)
  Thread.current.inheritable_thread_local_var_get(...)
end

def inheritable_thread_local_var_get(var_name)

treated the same as if #thread_variable? had returned false.
this means that a thread local variable with nil can't have any semantic meaning and should be
NOTE: because there's not a way to unset a thread variable, storing nil is used as deletion. 
def inheritable_thread_local_var_get(var_name)
  key = var_name.to_sym
  if @inheritable_thread_locals&.key?(key)
    @inheritable_thread_locals[key]
  else
    @thread_parent&.inheritable_thread_local_var_get(key)
  end
end

def inheritable_thread_local_var_set(...) 

def inheritable_thread_local_var_set(...)
  Thread.current.inheritable_thread_local_var_set(...)
end

def inheritable_thread_local_var_set(var_name, value) 

def inheritable_thread_local_var_set(var_name, value)
  @inheritable_thread_locals ||= {}
  @inheritable_thread_locals[var_name.to_sym] = value
end

def with_inheritable_thread_local_var(...) 

def with_inheritable_thread_local_var(...)
  Thread.current.with_inheritable_thread_local_var(...)
end

def with_inheritable_thread_local_var(key, value, &block) 

def with_inheritable_thread_local_var(key, value, &block)
  old_value = inheritable_thread_local_var_get(key)
  begin
    inheritable_thread_local_var_set(key, value)
    block.call
  ensure
    inheritable_thread_local_var_set(key, old_value)
  end
end