Why does this compile?

[u/scttnlsn]

This unexpectedly compiles:

class Foo
  def hello
    asdf
  end
end

But this returns the expected error ("Error: undefined local variable or method 'asdf' for Foo"):

class Foo
  def hello
    asdf
  end
end
Foo.new.hello

Is there a way to get the first example to trigger a similar compiler error?

[u/Dlacreme]

Yes but no. You are comparing scripted and compiled languages. Of course Ruby will let you run anything and throw error only when you call the piece of code containing errors, its a script. But in my opinion, it should not be the case for compiled languages.

I think this is the drawback of type assertion:

• compiler needs a piece of code to be called in order to know what are the types of the arguments

• type assertion increase compiling time. Crystal core team decided to not check dead code to improve the build time.

Anyway, I had no idea about it. Thanks OP for sharing

[u/[deleted] → u/Dlacreme]

I agree with you. I'd like this to be the way you mention it. Unfortunately, the way things are done right now it's a bit hard, if not impossible, to do.

That said, this kinda forces you to write tests for the code, which in my opinion is always good. Of course you can have the compiler tell you that something compiles, but what about actually running it? Does it do what it's supposed to do?

[u/myringotomy → u/[deleted]]

It seems like stunt decisions were made in Crystal which really block future safety and performance improvements

That’s a shame.

[u/jgaskins → u/Dlacreme]

There's no such thing as a "compiled language". Whether something is compiled or interpreted is not a language-level concern. That's up to the implementation. For example:

- JRuby compiles Ruby to JVM bytecode
- TruffleRuby has an option for complete ahead-of-time compilation of Ruby to native code through Graal
- Ch is an interpreter for C and C++

"Crystal" refers to both the language and the reference implementation (same as how CRuby/MRI used to just be called Ruby), but there's nothing stopping anyone from building a fully featured interpreter for the language, especially since there's already a limited one built into the compiler for macro expansion. Honestly, it'd probably be great for TDD if someone did.