Today I Learned

A Hashrocket project

12 posts by mattpolito @mattpolito

Safe Navigation on nil gotcha

tldr; Beware, both ActiveSupport’s try and Ruby’s safe navigation operator &. will always return nil when operating on a nil.

For example, I would have expected either to return a response like so:

> nil.try(:to_s) => ""
> nil&.to_s => ""

However this is not the case:

> nil.try(:to_s) => nil
> nil&.to_s => nil

Rounding Time in Increments

I Recently needed to round down a time in certain increments. This is not something I’ve ever been asked to do previously so it was an interesting problem to figure out. The resulting formula is simple:


This will give you the previous incremental minute. ex: Given a 5 minute increment @ 3:12, the result would be 10.

time =
new_min = time.min - (time.min % 5)

I happen to be solving this in a project with ActiveSupport so there was access to Time#change so I finished this up with:

time.change(min: new_min)

Turn on coordinates in Minecraft Realm

In a Minecraft Realm the option to turn on the coordinate system is not available without turning on cheats. That is not good because then you’ll lose achievements.

Many tutorials recommend downloading the realm locally, flipping the switch for coordinates, and then uploading that copy of your world back to the realm. Turns out that some server commands will work in the Realm… coordinates being one of them!

Enter this into your chat window to enable coordinates:

/gamerule showcoordinates true

You can, of course, turn them back off via:

/gamerule showcoordinates false

Find that change you know you made!

Sometimes you do awesome work…

Sometimes you even remember that awesome work when at a later point it is not there but everything in your being knows that you wrote it already.

Hopefully this will help:

git log --all --source -- path/to/my/file

This super useful command will show you changes on a particular file (that you totally know you changed) across branches; because sometimes our brains work so hard that we forget to get something merged and those important changes just sit there waiting to be useful again on another branch.

Keeping an SSH connection alive

Do you get disconnected from your SSH session often? I do… but I’ve found a solution that helps.

An SSH configuration that can be made on the server or client side but in my instance it makes more sense for the update to be on the client side.

In your ~/.ssh/config we’ll utilize the ServerAliveInterval declaration.

             Sets a timeout interval in seconds after which if no data has
             been received from the server, ssh(1) will send a message through
             the encrypted channel to request a response from the server.  The
             default is 0, indicating that these messages will not be sent to
             the server.  This option applies to protocol version 2 only.

This declaration informs the client to send a keep alive packet at a certain interval to the server, ensuring the connection stays open.

Host example
  ServerAliveInterval 30

That declaration will send a packet every 30 seconds if the connection goes idle. Now this is the desired funcationality that I’d like to see for all of my SSH connections so we can add it to the host wildcard like so:

Host *
  ServerAliveInterval 120

Truncate an Array

Every time I go to truncate and array in JavaScript, I have to look up the syntax. It’s something that makes me angry.

Did you know that there is an oddly easier way to do it without reaching for splice() or slice()?

const collection = [4,6,9,1,12,42];
collection.length = 3;

collection is now [4,6,9]

Hopefully I can remember this one!

Install `capybara-webkit`

Turns out capybara-webkit’s has a dependency on qtwebkit which has been removed from the qt library package. You’ll have the pleasure of finding this out when you run into this grand error:

Project ERROR: Unknown module(s) in QT: webkitwidgets

To get around this, you can install a previous version of qt using brew via:

brew install qt@5.5

Now reload your terminal and ensure that you can run qmake. Once that is all good, go ahead and reinstall/bundle capybara-webkit.

Don’t let this stump you for longer than it did me!

Using pessimistic gem version to catch betas

The trouble with pessimistic (~>) versioning is that it still won’t catch pre-release library versions… or will it.

It actually can allow ‘beta’ versions by adding an ‘x’ to the version you’d like to catch.

gem "rails", "~> 5.x"

Since ‘beta’ versions (5.0.0.beta3) actually register as higher than 5.0.0, the pessimistic operator will not catch the beta version. Gem versioning shows any version with a letter as ‘pre-release’ which is how beta3, rc1, alpha versions work.

Using the ‘x’ as a wildcard will allow pre-release gem versions to be caught.