Sophisticated semantics of Ruby

hoge.rb

class Hoge
   def a=(x)
      puts "Pooh!"
   end
   private "a=".intern

   def a
      puts "Bra!"
   end
   private :a

   def m0
      self.a = 100
   end

   def m1
      p a
   end

   def m2
      p self.a
   end
end

class Foo
   def m1
      p a
   end
end

x = Hoge.new
begin
   puts "-- Calling Hoge#m0"
   x.m0
rescue => e
   printf "> %s\n", e.inspect
end

begin
   puts "-- Calling Hoge#m1"
   x.m1
rescue => e
   printf "> %s\n", e.inspect
end

begin
   puts "-- Calling Hoge#m2"
   x.m2
rescue => e
   printf "> %s\n", e.inspect
end

begin
   puts "-- Accessing x.a="
   x.a = 100
rescue => e
   printf "> %s\n", e.inspect
end

y = Foo.new
begin
   puts "-- Calling Foo#m1"
   y.m1
rescue => e
   printf "> %s\n", e.inspect
end

def y.a()
   puts "Hahaha!!"
end

begin
   puts "-- Calling y.m1"
   y.m1
rescue => e
   printf "> %s\n", e.inspect
end

result.txt

$ ruby hoge.rb
-- Calling Hoge#m0
Pooh!
-- Calling Hoge#m1
Bra!
nil
-- Calling Hoge#m2
> #<NoMethodError: private method `a' called for #<Hoge:0x0000560e49600038>>
-- Accessing x.a=
> #<NoMethodError: private method `a=' called for #<Hoge:0x0000560e49600038>>
-- Calling Foo#m1
> #<NameError: undefined local variable or method `a' for #<Foo:0x0000560e4955d888>>
-- Calling y.m1
Hahaha!!
nil