Why doesn't every, and I mean it, language have this feature?

Question

Some time ago I had a look into Ruby and one of the things which stood out most for me was the way of using symbols.

While you to use defines or strings like in C++ or Python as an alternative, in Ruby you just write :mySymbol and the interpreter takes over the enumeration for you.

• I can't see any disadvantage this feature has, so why is it missing in say, PHP and Python?

Answer 1

One reason is that it's not as straightforward to implement in a compiled language such as C++.

Another one is that non-predefined symbols make it difficult to validate values on compile time. Having to pre-define the values prevents typos later, because they produce a compile-time error.