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Ruby Mistakes
=============

* Using blocks for looping and callbacks
  * break/next/return semantics in blocks extremely bizzare
  * And they have different behavior in procs vs. lambdas
* Why on earth does defined? return a string?
* throw/catch. Why!
* Inline rescue, no ability to specify what exception (and by extension, "catch
  anything" behavior common in community)
* Mutable objects have a hash method and can go in Hashes. Why!!!
* Extremely complex grammar, makes barrier to entry for implementation much
  higher
* Special case of flip-flop and regexp in an if statement (only if it appears
  syntactically though!)
* Setting `$=` to something truthy causes all string operations to become
  case-insensitive. This and other magic globals from perl are mind blowing.
* Keywords that silently override methods by the same name (defined?, on
  Rubinius block_given?)
* `f {}`. Tell me what the parsing of that is.
* proc, lambda, block, method, unbound method, functions. None of which have a
  clear relationship. set_trace_func exists, even though you can't pass
  functions around.
* Bizzare magic::
    def f
        Proc.new
    end
    f { |x| 3 }
  How does ``Proc.new`` know where the block came from?
* Ruby's module system makes namespacing optional (and off by default).
* Regexp with named matches decompose into local variables. Dear lord why.
* Encoding system is beyond broken
* Scopes: constants, class vars, instance vars, methods, locals. wtf.
* Constants aren't constant. Truth in naming.
* Thread locals are really fiber locals.
* You can change the encoding of a string. Just jesus christ wow.

Those are not so much mistakes. They may be really odd design decisions with hard-to-grasp semantics. They may be problematic because they make it hard to write efficient interpreters and/or compilers. They may be a problem to compiler implementors to the point where it is almost impossible to get the language right. But I do not think they are outright mistakes.

That said, what makes Ruby so appealing to others certainly does not appeal to me. It is not an aesthetic language to me, but to others it seems to be. I think this can be compared to a discussion about paintings: if you don't like the impressionistic style, then you don't like it.

And the compiler thing is real. If constants are not constants, then the compiler cannot propagate constant values and hence performance will suffer. And this is just one example of such.

@apeiros You can never be certain that the the hash key you pass to a function won't be mutated. Thus, the default of only allowing immutable (or at least frozen) keys is much less dangerous. Hash could even freeze the keys on the way in itself.

I see a fair about of people already argued by the majority of things in the list, so I'll just leave it there. I will make an addition to the statement about inline rescue though.

Inline rescue, no ability to specify what exception (and by extension, "catch
anything" behavior common in community)

@avdi talks about inline rescue in episode 22 of Ruby Tapas. Inline rescue might come handy if you want to evaluate the exception and act upon it. This can be done by making use of the $! variable.

Inline rescue, no ability to specify what exception (and by extension, "catch anything" behavior common in community)

This is the worst IMHO; the others are not so bad (the one of the Regexp with named matches is bad, but is not so common), and some are just "not bugs but features" (f.e. the fact that you can change the encoding of a string).

Python guy complaining that Ruby isn't Python. It shouldn't be "Ruby Mistakes". It should be "Things about Ruby I don't understand because it doesn't work the same way as in a language I'm used to".

@cogweh If it should be "Things about Ruby I don't understand..." than could you be so kind to share a part of your genuine experience with ruby and explain those things to us, python/javascript/lisp/whatever guys.

A corresponding Python Mistakes gist :)
https://gist.github.com/4558963

This reminds me of the blub paradox...

@Nek selective context "...because it doesn't work the same way as in a language I'm used to" This is basically frivolous bickering about the language which we shouldn't be having. The OP is clearly trying to point out what he perceives as flaws in a language without much basis. It's the same thing as saying "that car is red so it must be horrible."