TIL

‘Random’ numbers in Go don’t always seem random. This is because the rand package defaults to a seed of 1. That’s great if you need a bunch of random numbers at the start of your program. Not great if you expect a different outcome each time you run the program. A solution is to seed rand with Unix time. Try it in the init() function: package main import ( "math/rand" "time" ) func init() { rand.Seed(time.Now().UTC().UnixNano()) } ...

Want to build URLs with JavaScript? Try thewindow.location object. This came from a React.js project we’re working on. It uses ES6 template string interpolation, which isn’t necessary but definitely is nice: `${window.location.protocol}//${window.location.host}/posts/${this.props.postID}/edit` Which becomes: "https://secret-project.com/posts/42/edit"

Using a Postgres table for caching? You might want to try making it unlogged. unlogged tables are not written to the write-ahead log, which makes them much faster. This also means they are not crash-safe, and are truncated when a crash or unclean shutdown occurs. For caching purposes, that’s likely to be an acceptable tradeoff. Documentation

Go has an interesting feature called iota. When declaring a list of constants, this keyword represents successive untyped integer constants. const ( foo = iota // foo == 0 bar = iota // bar == 1 baz = iota // baz == 2 ) Anytime const is invoked, the counter resets. const foo = iota // foo == 0 const bar = iota // bar == 0 This is a cool way to quickly define a list of integer constants, such as ’true’ and ‘false’, for later use.

Ruby has a nice percent string literal for regular expressions, %r. It’s like // but allows your regex to contain backslashes without escaping them. Check it out: 2.1.0 :001 > 'http://google.com'.gsub(/http:\/\/google.com/, 'fine') => "fine" 2.1.0 :002 > 'http://google.com'.gsub(%r{http://google.com}, 'better') => "better" As the example implies, this is useful when matching URLs. Documentation

You can store a PostgreSQL query with prepare. db=# prepare posts_search as select title from posts limit 5; PREPARE Call the method with execute. db=# execute posts_search; title ----------------------------------- Hello World! My First Pull Request: HAML My First Pull Request: Sinatra My First Pull Request: Capistrano My First Pull Request: SASS (5 rows) Deallocate the query with deallocate, and you can set it again. db=# deallocate posts_search; DEALLOCATE db=# prepare posts_search as select title from posts limit 10; PREPARE

Want to change database connections from inside psql? You can! Psql, the REPL for Postgres, has a useful meta-command called \connect, or \c. This lets you establish a new connection to a Postgres server, while closing the current connection. Here is the required format: \c or \connect [ dbname [ username ] [ host ] [ port ] ] | conninfo Only \c [my_database] is required; omitted parameters are taken from the previous connection. ...

To maintain data integrity, certain actions like rake db:drop will not execute when there are active sessions on a Postgres database. You’ll get an error like this: ERROR: database "database_name" is being accessed by other users DETAIL: There are 2 other session(s) using the database. Sessions can be killed from the command line, but a safer route is to kill them with a database method. First, revoke all public access from the database: ...

The Ruby keyword not and the unary ! aren’t the same. They have a different precedence, and therefore are not interchangeable, despite seeming very similar. irb > not 3 == 4 => true irb > !3 == 4 => false The first example is evaluated as not (3 == 4), or not false, which is true. The second example is evaluated as (not 3) == 4, or false == 4, which is false. ...

Ruby has a few interesting old keywords that use the underscore, or ‘skid’, to convey meta information about the file. Here they are in action: # test.rb puts __ENCODING__ puts __FILE__ puts __LINE__ __END__ Because this is after 'end', it should not be executed Running this file produces: $ ruby test.rb UTF-8 test.rb 3 Pretty cool!