Accessing values in nested hash securly (without tripping over nil)?

Question

Given:

array = {first: {second: {one: 1, two: 2, three: 3 }}}

assuming anything can be nil, what would be the simplest/most concise way to access the nested values without tripping over nil? If any of the members doesn't exist, it should just return nil.

We came up with these:

Pure Ruby:

value = array.fetch(:first, {}).fetch(:second, {}).fetch(:four, nil)
value = begin array[:first][:second][:four]; rescue; end

Ruby on Rails:

value = array.try(:[], :first).try(:[], :second).try(:[], :four)

What can you come up with? Which method would you prefer, and why?

Thanks!

sawa · Accepted Answer · 2013-06-06T06:20:56.340

1

It is matter of coding style. With Ruby 2.0, you can also do this, which I may like better:

value = array[:first].to_h[:second].to_h[:four]

If you do not want to type to_h each time, you can define a method:

class Hash
  def safe_fetch k; self[k].to_h end
end
value = array.safe_fetch(:first).safe_fetch(:second)[:four]

edited Jun 06 '13 at 06:20

answered Jun 06 '13 at 01:56

sawa

165,429
45
277
381

Any idea how to define and use the `safe_fetch` method inside a Rails 5 application? – W.M. Sep 02 '17 at 21:09

score -2 · Answer 2 · answered Jun 05 '13 at 16:20

-2

I will prefer inline rescue, as it is more Rubyistic.

array = {first: {second: {one: 1, two: 2, three: 3 }}}
value = array[:first][:second][:four] rescue nil # => nil
value = array[:first][:second][:two] rescue nil # => 2

answered Jun 05 '13 at 16:20

Arup Rakshit

116,827
30
260
317

1

nice, didn't know that the rescue one could be shortened – Sascha Kaestle Jun 05 '13 at 16:23
5

A blind `rescue` is playing with fire and should be avoided whenever possible. – tadman Jun 05 '13 at 16:27

Accessing values in nested hash securly (without tripping over nil)?

2 Answers2