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# cjavdev's solution

## to Space Age in the Elixir Track

Published at Jul 13 2018 · 2 comments
Instructions
Test suite
Solution

#### Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Given an age in seconds, calculate how old someone would be on:

• Earth: orbital period 365.25 Earth days, or 31557600 seconds
• Mercury: orbital period 0.2408467 Earth years
• Venus: orbital period 0.61519726 Earth years
• Mars: orbital period 1.8808158 Earth years
• Jupiter: orbital period 11.862615 Earth years
• Saturn: orbital period 29.447498 Earth years
• Uranus: orbital period 84.016846 Earth years
• Neptune: orbital period 164.79132 Earth years

So if you were told someone were 1,000,000,000 seconds old, you should be able to say that they're 31.69 Earth-years old.

If you're wondering why Pluto didn't make the cut, go watch this youtube video.

## Running tests

Execute the tests with:

``````\$ elixir space_age_test.exs
``````

### Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.

For example:

``````# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
``````

Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the test suite.

``````# ExUnit.configure exclude: :pending, trace: true
``````

For more detailed information about the Elixir track, please see the help page.

## Source

Partially inspired by Chapter 1 in Chris Pine's online Learn to Program tutorial. http://pine.fm/LearnToProgram/?Chapter=01

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### space_age_test.exs

``````if !System.get_env("EXERCISM_TEST_EXAMPLES") do
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

# You need to define a SpaceAge module containing a function age_on that given a
# planet (:earth, :saturn, etc) and a number of seconds returns the age in years
# on that planet as a floating point number.

defmodule SpageAgeTest do
use ExUnit.Case

# @tag :pending
test "age on Earth" do
input = 1_000_000_000
assert_in_delta 31.69, SpaceAge.age_on(:earth, input), 0.005
end

@tag :pending
test "age on Mercury" do
input = 2_134_835_688
assert_in_delta 67.65, SpaceAge.age_on(:earth, input), 0.005
assert_in_delta 280.88, SpaceAge.age_on(:mercury, input), 0.005
end

@tag :pending
test "age on Venus" do
input = 189_839_836
assert_in_delta 6.02, SpaceAge.age_on(:earth, input), 0.005
assert_in_delta 9.78, SpaceAge.age_on(:venus, input), 0.005
end

@tag :pending
test "age on Mars" do
input = 2_329_871_239
assert_in_delta 73.83, SpaceAge.age_on(:earth, input), 0.005
assert_in_delta 39.25, SpaceAge.age_on(:mars, input), 0.005
end

@tag :pending
test "age on Jupiter" do
input = 901_876_382
assert_in_delta 28.58, SpaceAge.age_on(:earth, input), 0.005
assert_in_delta 2.41, SpaceAge.age_on(:jupiter, input), 0.005
end

@tag :pending
test "age on Saturn" do
input = 3_000_000_000
assert_in_delta 95.06, SpaceAge.age_on(:earth, input), 0.005
assert_in_delta 3.23, SpaceAge.age_on(:saturn, input), 0.005
end

@tag :pending
test "age on Uranus" do
input = 3_210_123_456
assert_in_delta 101.72, SpaceAge.age_on(:earth, input), 0.005
assert_in_delta 1.21, SpaceAge.age_on(:uranus, input), 0.005
end

@tag :pending
test "age on Neptune" do
input = 8_210_123_456
assert_in_delta 260.16, SpaceAge.age_on(:earth, input), 0.005
assert_in_delta 1.58, SpaceAge.age_on(:neptune, input), 0.005
end
end``````
``````defmodule SpaceAge do
@type planet :: :mercury | :venus | :earth | :mars | :jupiter
| :saturn | :neptune | :uranus

@orbital_periods %{
:mercury => 0.2408467,
:venus => 0.61519726,
:earth => 1,
:mars => 1.8808158,
:jupiter => 11.862615,
:saturn => 29.447498,
:uranus => 84.016846,
:neptune => 164.79132
}

@doc """
Return the number of years a person that has lived for 'seconds' seconds is
aged on 'planet'.
"""
@spec age_on(planet, pos_integer) :: float
def age_on(planet, seconds) do
seconds / (@orbital_periods[planet] * 31557600)
end
end``````

:smile: Hiya CJ!

Nice. I had forgotten Map#[] and Map.fetch() behave differently.

One suggestion I have is that it's not clear from the code where 31557600 comes from. You could perhaps extract the calculation, e.g. @days_in_earth_year 365.25 @seconds_in_an_hour 60 @minutes_in_an_hour 60 @hours_in_a_day 24 @seconds_in_earth_day @seconds_in_an_hour * @minutes_in_an_hour * @hours_in_a_day

### What can you learn from this solution?

A huge amount can be learned from reading other peopleâ€™s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?