lll

lll

lll() is used in debugging to display an expression and its value.

Motivation

One of the most basic tools in debugging is printing out the values of variables (or other expressions) during program execution:

puts user_name

Sometimes you need to label these values so you know what they're referring to, especially if you're outputting a lot of them:

puts "user_name = #{message}"

lll() does the labelling automatically:

lll{'user_name'}

The expression is passed as a string inside a block. It's useful to create a text editor macro that outputs lll{''} and leaves the cursor inside the apostrophes.

Other benefits

Output goes to standard output and the Rails log (if available).

Output is displayed in reverse video, so it's easy to pick out from the log or console.

lll() uses #inspect to output the expression. It outputs Enumerable members (except strings) on separate lines.

If Awesome Print is available on your system, lll() uses it.

Output is tagged with the file and line number where it appears, so you can easily find lll's that you forgot to take out. The time of day (but not the date) is also printed, so you don't waste time looking at old output.

Outputting additional text

Sometimes you want to include some other string, along with the label and value like this:

puts "After polling the queue, user_name = #{user_name}"

You can pass a string to lll() to print a string:

lll("After polling the queue"){'user_name'}

And because lll() outputs in reverse video, and to the Rails log, it can be useful to simply print a string without an expression:

lll "After read_user"