23 May 2012
I’ve been trying to expand my ruby toolset. The other day I had thirty minutes to try out ruby-debug and failed. I couldn’t get it operational, and I ended up here in a sad state of affairs. How could the ruby debugger be languishing in the latest ruby versions? I think last night I may have figured out why. The why is Pry.
A Live State and Code Explorer
Calling up Pry reminded me of my sweet, sweet, beloved Smalltalk. If you’re not familiar, Smalltalk is a magical land of rainbows and hot-air balloons, where objects dance and sing, and you can munch bite-sized clouds of cotton- candy code all day long. Developing in Smalltalk, exploring the state and protocol of live objects is simple and embedded and constant. It’s all about digging in and discovery, and Pry lets you do that ( sans mouse to boot ).
A Pry Story
I’m learning cucumber. I writing step definitions in this DSL and it feels a little like a foreign land. In my step definitions, I have objects like “page” available to me and I don’t even know what they are. And I wouldn’t care, until I’m trying test the contents of a Google calendar embedded in an iframe, complicated.
So I want to explore “page”. I put the line below in my step definition:
Then, running cucumber invoked the Pry REPL:
So it turns out “pages” are Cabybara::Sessions. What methods can I call on them?
pry(#<Capybara::Session>)> ls Capybara::Session#methods: all app attach_file body check choose cleanup! click_button click_link click_link_or_button click_on current_host current_path current_url document driver evaluate_script execute_script field_labeled fill_in find find_button find_by_id find_field find_link first has_button? has_checked_field? has_content? has_css? has_field? has_link? has_no_button? has_no_checked_field? has_no_content? has_no_css? has_no_field? has_no_link? has_no_select? has_no_selector? has_no_table? has_no_unchecked_field? has_no_xpath? has_select? has_selector? has_table? has_unchecked_field? has_xpath? html inspect mode reset! reset_session! response_headers save_and_open_page save_page select source status_code text uncheck unselect visit wait_until within within_fieldset within_frame within_table within_window self.methods: __binding_impl__ instance variables: @app @document @driver @mode @scopes locals: _ _dir_ _ex_ _file_ _in_ _out_ _pry_
(This actually looks like a Smalltalk class definition to me.)
Browsing the protocol…”body” looks about right:
pry(#<Capybara::Session>)> body => "<!DOCTYPE html> <html><head>
That’s what I needed to get to. So in three quick steps I figured out:
- the class of “page”
- what methods I could call on “page”
- the current state “page”
Coding Through Discovery
And that’s everything I wanted to know. The beautiful thing is that never did I have to scour through API documentation to figure out the the simplest use- cases for this class. The output is clean and the environment is optimized for discovery.
I’m only scratching the surface here. As a runtime-invoked REPL and debugger, it’s certainly doing the trick. But I’ve gathered another huge part of what Pry provides is good tools for source and documentation browsing. Pry’s tagline is “Get to the code”.
Pry and Rails
You can use Pry in place of rails console by loading your rails app’s environment into Pry like:
pry -r ./config/environment
I’m really interested in exploring the ability to call pry from within the context of a running Rails app. I’m not sure if this is a thing, it would be so helpful to pop up a pry REPL from, say, a controller action. Believe me, I’ve tried.
Oh, and pry remembers my command history between sessions, cough irb.
I can’t speak to ruby-debug, maybe it does similar things, but I suspect the reason it failed to install for me is that everyone’s discovered Pry. You should too. Thanks @p9k for re-kindling my interest in this.