Gradual type checking for Ruby

[curryhoward]

When most practitioners think of "typechecking", they typically think about proving properties about programs statically. This project seems equivalent to adding a runtime check at each call site to ensure the arguments and return values are the correct type.

This is certainly useful sometimes, as it gives programs the desirable "fail fast" property. But it isn't "typechecking" as most engineers understand it. Or at least, it should be clarified that this is run-time typechecking. As such, it negatively impacts runtime performance, unlike compile-time typechecking.

This project also seems to miss the primary opportunity of run-time type checking: checking properties that are difficult to prove statically! For example, checking that a number is even, that a string is lowercase, that an index is within the bounds of an array, etc. These exotic types require a dependent type system to be checked statically, but in a dynamic environment they are trivial to verify.

Two suggestions for improvement: 1) add "sum" types (i.e., discriminated unions), and 2) let the user define their own types via lambdas, such as PrimeNumber.

[girvo]

> When most practitioners think of "typechecking", they typically think about proving properties about programs statically. This project seems equivalent to adding a runtime check at each call site to ensure the arguments and return values are the correct type.

It basically seems equivalent (albeit somewhat nicer in a few ways, ie. scalar types are supported) to PHP's "type hinting"[0]. I will say that it is useful, in combination with unit testing, as you can pick up on problems with things slightly easier than hoping for the best in production and tailing error logs, but proper static type analysis is more useful.

[0] http://php.net/manual/en/language.oop5.typehinting.php

[rtpg]

One thing we've applied on a Python(2, unfortunately, so can't go deep on the static type analysis) is enable this sort of type hinting when running our app in debug or test mode. Obviously can't catch everything, but it catches some of the sillier bugs.

[seanmcdirmid]

This is kind of pedantic. What programmers think of and find useful as types and type systems is quite different from what type theorists think.

[Mithaldu]

> This gem brings you advantage of type without changing existing code's behavior.

I'm fairly sure it changes the performance characteristics of code it is applied on. I'd recommend adding benchmarks to the README so prospective users might be aware of this beforehand.

[vidarh]

As someone working on a Ruby AOT compiler (whether it'll ever be finished is another matter...), I'd love to get some spec'ed out extensions for things like this with semantics that explicitly allows implementations to recognise the extension and decide to ignore the default implementation and instead provide it's own version that could e.g. do compile time checks instead of runtime checks, or hoist checks, whenever possible. Or use it for optimisations (e.g. by hoisting out and eliminating other checks and caching method lookups)

Ruby is flexible enough to allow quite a bit of experimentation with stuff like that. Especially because classes can be re-opened, so if worried about performance, it'd be easy enough to allow type annotations (or whatever other extensions people come up with) to live in separate files if people want them to, and conditionally include them only as needed/wanted.

[overload119]

This.

[JoelMcCracken]

This is very similar to contracts.ruby, which is cool. I'd love for more contract discussions.

https://github.com/egonSchiele/contracts.ruby

[MrDosu]

Personally I don't get contracts when they aren't used for static verification.

It's much easier to use defensive coding techniques at runtime without having yet another framework in there that anyone who wants to read the code has to learn. Typing a few lines less is not really a benefit when it basically increases code complexity.

[anaolykarpov]

I find that putting the method signature at the end of the method definition can become unreadable pretty fast. Also, the fact that it doesn't offer any performance improvement (most probably, this will actually degrade performance) makes me see this as a cool trick, but not really recommended in production.

I like the aproach Perl 6 took on gradual typing. You can read about it in this article which computes fibonnaci's number:http://blogs.perl.org/users/ovid/2015/02/avoid-a-common-soft...

The only reason I wait for the next winter to come is because Perl6 will be production ready by then as Larry Wall announced at FOSDEM this year.

[arnvald]

Since Ruby 2.1 (IIRC), method definition returns symbol, therefore it's possible to something like

typesig def meth(arg) arg end, [Numeric] => Numeric

Although it's still end of the method, it already suggests that signature will be there

[cookrn]

I wonder if it would be possible to configure this gem with "environments" in the same way that Rails applications have environments. Then, in development/test/CI-like environments, very strict checking could be applied based on the specified types. Otherwise, in production-like environments where "performance" may be more important, the type-checking could be looser or simply pass-through.

Disclosure: this may be a Bad Idea (TM)

[moe]

This already exists in a relatively mature form: https://github.com/egonSchiele/contracts.ruby

[nahiluhmot]

Really cool idea! I like that you can specify a `#respond_to?` constraint instead of a class. Not sure if OP is the author, but here's some feedback:

* It would be better if this didn't pollute the global namespace by defining `#typesig` in `Module` [0] -- perhaps consider refactoring that method into a module which the user may extend. Doing so would also get you out of needing to define `Module#prepend` for older versions of Ruby.

* Perhaps allow the user to enable/disable type checking at a global/class level. For example, then users could only enable type checking during specs if they wanted.

* Instead of using class-level variables, try using class level instance variables. They have less odd behavior when dealing with subclasses [1].

[0] https://github.com/gogotanaka/Rubype/blob/develop/lib/rubype...

[1] http://www.sitepoint.com/class-variables-a-ruby-gotcha/

Edit: Whitespace

[riffraff]

there are respond_to? constraint, the first example is

    typesig :sum, [:to_i, Numeric] => Numeric

notice the :to_i

also, the global switch is simple:

    if $DEBUG
      require 'rubype'
    else
      def typesig(*args) end
    end

:)

[saraid216]

> Not sure if OP is the author

The OP is eduardordm, which can be found right underneath the article link. If you look on his HN profile, his GitHub name is also eduardordm.

The repo author is gogotanaka.

So, no. He's not. And the repo author is consequently unlikely to ever see your comments.

Not only are these simple checks to make, but it's extremely bad practice to scatter commentary about a project everywhere across the internet; people who only know about this project through GitHub would not see your comments either.

[jaggederest]

Reminds me of https://github.com/lucky/pedant from a few years ago. I added some basic argument assertions to it as well: https://github.com/lucky/pedant/pull/1

[overload119]

I've been writing Ruby for a few years on a number of production applications.

Recently I've had to pickup Hack for work, and if there's one thing I really like about it is the type hinting. The best part is that it helps you handle nullable types (not sure if it's done here).

When I switch back to Ruby from Hack, I find it harder to reason about my program.

[firlefans]

More interesting to my mind is this (Diamondback Ruby):

http://www.cs.umd.edu/projects/PL/druby/

Some features:

--------------

Type inference:

DRuby uses inference to model most of Ruby’s idioms as precisely as possible without any need for programmer intervention.

Type annotations:

Methods may be given explicit type annotations with an easy to use syntax inspired by RDoc.

Dynamic checking:

When necessary, methods can be type checked at runtime, using contracts to isolate and properly blame any errant code, similar to gradual typing.

Metaprogramming support:

DRuby includes a combined static and dynamic analysis to precisely model dynamic meta-programming constructs, such as eval and method_missing.

[siscia]

Any now and then another language get some sort of type check, why we don't build an agnostic type checker ?

Then we interface with the AST of any language and we can stop re-iventing the wheel every two week...

It is so crazy ?

Nobody tried it before ?

[vinceguidry]

Type checking is typically done statically, i.e. during compile time. By the time you have AST it's too late.

Think about it, how would you handle type annotations in an agnostic type checker?

[stewbrew]

IMHO the state of static type checking/code analysis in ruby is still deplorable and this (well known, rather trivial) approach won't ameliorate the situation. Even javascript has more to offer in this respect. Who would have suspected that 5 years ago.

Since I still like ruby's syntax, my hopes are that crystal (http://crystal-lang.org/) will one day become more mainstream (and maybe be adapted to some extent in mainstream ruby).

[transfire]

Already done many years ago: https://github.com/rubyworks/platypus

[shitlord]

Is there an error in the section named "Typed method can coexist with non-typed method"? There's a line that has `typesig :sum` but sum is never defined.

[revskill]

Why Ruby 2.0 ?

[damncabbage]

In case the question is actually "Why not 1.9.3?", it's likely because 1.9.3 is End Of Life, and doesn't even get security upgrades now:

https://www.ruby-lang.org/en/news/2014/01/10/ruby-1-9-3-will...

https://www.ruby-lang.org/en/news/2015/02/23/support-for-rub...