Today in our continued journey through our **Ruby Exception Handling** series we'll be taking a closer look at the `ZeroDivionError`

. As you may suspect the `ZeroDivisionError`

occurs when attempting to divide a number by zero.

In this article we'll briefly explore the `ZeroDivisionError`

in more detail, including where it sits within the Ruby `Exception`

class hierarchy and showing a few simple code examples to illustrate how `ZeroDivisionErrors`

occur in the first place. Let's get started!

## The Technical Rundown

- All Ruby exceptions are descendants of the
`Exception`

class, or a subclass therein. `StandardError`

is a direct descendant of the`Exception`

class, and is also a superclass with many descendants of its own.`ZeroDivisionError`

is the direct descendant of`StandardError`

.

## When Should You Use It?

Producing a `ZeroDivisionError`

is quite simple, but there are a few small quirks that you'll want to be aware of before assuming your `rescue ZeroDivisionError => e`

statement will always catch attempts to divide by zero-ish values. To illustrate we have a few example methods showing normal division, division by exactly zero, division by floating zero, and division by negative floating zero. As usual we'll start with the full code snippet and then we'll briefly go through it to see what's going on:

`def execute_examples`

division_example

Logging.line_separator

zero_division_example

Logging.line_separator

floating_zero_division_example

Logging.line_separator

negative_floating_zero_division_example

enddef division_example

begin

# Set the numerator.

numerator = 15

# Set the denominator.

denominator = 5

# Divide and output the result.

Logging.log(numerator / denominator)

#=> 3

rescue ZeroDivisionError => e

Logging.log(e)

rescue => e

Logging.log(e, { explicit: false })

end

enddef zero_division_example

begin

# Set the numerator.

numerator = 15

# Set the denominator to zero.

denominator = 0

# Try to divide and output the result.

Logging.log(numerator / denominator)

#=> (EXPLICIT) ZeroDivisionError: divided by 0

rescue ZeroDivisionError => e

Logging.log(e)

rescue => e

Logging.log(e, { explicit: false })

end

enddef floating_zero_division_example

begin

# Set the numerator.

numerator = 15

# Set the denominator to zero as float.

denominator = 0.0

# Try to divide and output the result.

Logging.log(numerator / denominator)

#=> Infinity

rescue ZeroDivisionError => e

Logging.log(e)

rescue => e

Logging.log(e, { explicit: false })

end

enddef negative_floating_zero_division_example

begin

# Set the numerator.

numerator = 15

# Set the denominator to negative zero as float.

denominator = -0.0

# Try to divide and output the result.

Logging.log(numerator / denominator)

#=> -Infinity

rescue ZeroDivisionError => e

Logging.log(e)

rescue => e

Logging.log(e, { explicit: false })

end

end# Execute examples.

execute_examplesmodule Logging

extend Utilityclass << self

# Outputs +value+ to console.

# +args+ may include:

# +:explicit+ (Boolean) - Is +Exception+ class +value+ expected? [default: true]

# +:timestamp+ (Boolean) - Should timestamp be included? [default: false]

#

# Examples:

#

# Logging.log('My message') #=> "My message"

# Logging.log('My message', { timestamp: true} ) #=> "[12:00:05] My message"

#

# begin

# raise Exception.new('An exception!')

# rescue Exception => e

# Logging.log(e)

# end

# #=> (EXPLICIT) Exception: An exception!

# #=> (...backtrace...)

def log(value, args = {})

# Check if exception was explicit.

explicit = args[:explicit].nil? ? true : args[:explicit]

# Get timestamp if necessary.

timestamp = args[:timestamp] ? formatted_timestamp : ""if value.is_a?(Exception)

# If +value+ is an +Exception+ type output formatted exception.

puts timestamp << formatted_exception(value, explicit)

elsif value.is_a?(String)

# If +value+ is a +String+ directly output

puts timestamp << value

else

# If +value+ is anything else output.

puts timestamp if !timestamp.empty?

puts value

end

end# Output the specified +separator+ +count+ times to log.

# +args may include:

# +:count+ (Integer) - Number of characters to output. [default: 20]

# +:separator+ (String) - Character or string to duplicate and output. [default: '-']

def line_separator(args = {})

count = args[:count].nil? ? 20 : args[:count]

separator = args[:separator].nil? ? '-' : args[:separator]# Concatenate and output.

puts separator * count

endprivate

def formatted_exception(exception, explicit)

# Set explicit or inexplicit tag.

output = "(#{explicit ? 'EXPLICIT' : 'INEXPLICIT'}) "

# Add class and message.

output << "#{exception.class}: #{exception.message}\n"

# Append backtrace with leading tabs.

output << "\t" << exception.backtrace.join("\n\t")

# Return output string.

output

end

`def formatted_timestamp`

"[#{Time.now.strftime("%T")}] "

end

end

end

We start with a normal and functional `#division_example`

method:

`def division_example`

begin

# Set the numerator.

numerator = 15

# Set the denominator.

denominator = 5

# Divide and output the result.

Logging.log(numerator / denominator)

#=> 3

rescue ZeroDivisionError => e

Logging.log(e)

rescue => e

Logging.log(e, { explicit: false })

end

end

This works as expected and outputs a result of `3`

. However, if we change our `denominator`

to `0`

we'll produce a `ZeroDivisionError`

, as seen in `#zero_division_example`

:

`def zero_division_example`

begin

# Set the numerator.

numerator = 15

# Set the denominator to zero.

denominator = 0

# Try to divide and output the result.

Logging.log(numerator / denominator)

#=> (EXPLICIT) ZeroDivisionError: divided by 0

rescue ZeroDivisionError => e

Logging.log(e)

rescue => e

Logging.log(e, { explicit: false })

end

end

That should make sense to most of us I think: Just like when you were bored in school and were messing around with your calculator and tried dividing by zero you'd get an error, the same applies in Ruby (and probably all other programming languages for that matter). However, dividing by zero in all cases may not work exactly as you'd think. Watch what happens when we change our denominator from `0`

to a floating point representation of `0.0`

:

`def floating_zero_division_example`

begin

# Set the numerator.

numerator = 15

# Set the denominator to zero as float.

denominator = 0.0

# Try to divide and output the result.

Logging.log(numerator / denominator)

#=> Infinity

rescue ZeroDivisionError => e

Logging.log(e)

rescue => e

Logging.log(e, { explicit: false })

end

end

Suddenly we no longer produce a `ZeroDivisionError`

but, instead, we get an output of `Infinity`

. This is because Ruby handles various numeric data object types differently: whole numbers or `Integers`

like `0`

are calculated differently than `Floats`

like `0.0`

.

We can see this strangeness continue if we change the `denominator`

from `0.0`

to the negative version of `-0.0`

, which produces an output of *negative* `Infinity`

:

`def negative_floating_zero_division_example`

begin

# Set the numerator.

numerator = 15

# Set the denominator to negative zero as float.

denominator = -0.0

# Try to divide and output the result.

Logging.log(numerator / denominator)

#=> -Infinity

rescue ZeroDivisionError => e

Logging.log(e)

rescue => e

Logging.log(e, { explicit: false })

end

end

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