Is Ruby really an interpreted language if all of its implementations are compiled into bytecode?

Question

In the chosen answer for this question about Blue Ruby, Chuck says:

All of the current Ruby implementations are compiled to bytecode. Contrary to SAP's claims, as of Ruby 1.9, MRI itself includes a bytecode compiler, though the ability to save the compiled bytecode to disk disappeared somewhere in the process of merging the YARV virtual machine. JRuby is compiled into Java .class files. I don't have a lot of details on MagLev, but it seems safe to say it will take that road as well.

I'm confused about this compilation/interpretation issue with respect to Ruby.

I learned that Ruby is an interpreted language and that's why when I save changes to my Ruby files I don't need to re-build the project.

But if all of the Ruby implementations now are compiled, is it still fair to say that Ruby is an interpreted language? Or am I misunderstanding something?

Answer 1

You can run Ruby programs interactively using irb, the Interactive Ruby Shell. While it may generate intermediate bytecode, it's certainly not a "compiler" in the traditional sense.

Answer 2

Yes, Ruby's still an interpreted language, or more precisely, Matz's Ruby Interpreter (MRI), which is what people usually talk about when they talk about Ruby, is still an interpreter. The compilation step is simply there to reduce the code to something that's faster to execute than interpreting and reinterpreting the same code time after time.

Answer 3

A compiled language is generally compiled into machine code, as opposed to just byte code. Some byte code generators can actually further compile the byte code into machine code though.

Byte code itself is just an intermediate step between the literal code written by the user and the virtual machine, it still needs to be interpreted by the virtual machine though (as it's done with Java in a JVM and PHP with an opcode cache).

Answer 4

Nearly every language is "compiled" nowadays, if you count bytecode as being compiled. Even Emacs Lisp is compiled. Ruby was a special case because until recently, it wasn't compiled into bytecode.

I think you're right to question the utility of characterizing languages as "compiled" vs. "interpreted." One useful distinction, though, is whether the language creates machine code (e.g. x86 assembler) directly from user code. C, C++, many Lisps, and Java with JIT enabled do, but Ruby, Python, and Perl do not.

People who don't know better will call any language that has a separate manual compilation step "compiled" and ones that don't "interpreted."

Answer 5

This is possibly a little off topic but...

Iron Ruby is a .net based implementation of ruby and therefore is usually compiled to byte code and then JIT compiled to machine language at runtime (i.e. not interpreted). Also (at least with other .net languages, so I assume with ruby) ngen can be used to generate a compiled native binary ahead of time, so that's effectively a machine code compiled version of ruby code.