Ruby: two ways using try in Hash

Question

I want to extract a value by using try in Ruby.

I found there are two ways of doing this and was playing around with it in irb.

>> hash = { a: 1, b: 2 }
=> {:a=>1, :b=>2}
>> hash.try(:a)
=> nil
>> hash.try(:[], :a)
=> 1

I have two questions,

1. What is the difference between hash.try(:[], :a) and hash.try(:a)? I searched around and found people use both ways.
2. I saw a lot of places using hash.try(:a) to retrieve values, but why my trial returns nil?

Answer 1

hash.try(:[], :a)
# 1

Tries to invoke the public method [] on hash passing as :a as argument to []. As :a is an existing key in the hash, it returns its value.

hash.try(:a)
# nil

Tries to invoke the public method :a on hash. As hash as the receiver doesn't respond to :a then it returns nil.

As a clarification, the arguments for try are as first the method to be invoked on the receiver, and all the other arguments are the arguments for the method being invoked.

---

If your hash could respond to the method :a, hash.try(:a) would return the value of that method being called on hash:

# Just for example purposes
class Hash; def a; :a_monkey_patched_value_for_a; end

hash.try(:a)
# :a_monkey_patched_value_for_a