Avoiding nil errors

[Lomanu4]

Here is a quick way to avoid nil errors and get better failures in Ruby and Ruby on Rails. Convert hashes with known keys into Structs:


data = { a: 1, b: 2, c: 3}
...
MyData = Struct.new(:a,:b,:c)
data = MyData.new(a: 1, b: 2, c: 3)

Structs will throw if you introduce a typo instead of returning nil. This tightens your feedback loops and reduces debugging time.


hash[:d] => nil
struct[:d] => in 'Struct#[]': no member 'd' in struct (NameError)

That is cool. What about in more fluid situations like user input? You can convert arbitrary incoming hashes into known structs quickly with the following:


params = {a: 1, b: 2, c: 3, x: 9, z: 0}
MyData.new(**params.slice(*MyData.members))
Pitfalls


While Structs have much the same interface as hashes, there are some tricky differences.

• Hash#each is equivalent to Struct#each_pair.
• Hash#keys is equivalent to Struct#members.
• There is no equivalent to Hash#fetch.

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