Class: Danom::Maybe

Inherits:
Monad
  • Object
show all
Defined in:
lib/danom/maybe.rb

Instance Method Summary collapse

Methods inherited from Monad

#initialize, #monad_value, #value, #~@

Constructor Details

This class inherits a constructor from Danom::Monad

Dynamic Method Handling

This class handles dynamic methods through the method_missing method in the class Danom::Monad

Instance Method Details

#and_then ⇒ Maybe

Allows for safe navigation on nil.

nil&.m1&.m2&.m3 #=> nil

~Maybe(nil).m1.m2.m3 #=> nil

Using a Maybe really shines when accessing a hash

~Maybe({})[:person][:name].downcase.split(' ').join('-') #=> nil

{}.dig(:person, :name)&.downcase.&split(' ')&.join('-') #=> nil

Using #and_then without the Monad#method_missing sugar is also useful if you need to pass your value to another method

Maybe(nil).and_then{ |value| JSON.parse(value) } #=> Maybe

The block only gets executed if value is not ‘nil`

Returns:

See Also:

  • Danom::Monad#method_missing


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# File 'lib/danom/maybe.rb', line 26

def and_then
  if @value
    Maybe.new yield(@value)
  else
    Maybe.new(nil)
  end
end

#continue ⇒ Monad

“Fails” a maybe given a certain condition. If the condition is ‘false` then Maybe(nil) will be returned. Useful for performing side-effects given a certain condition

Maybe([]).and_then do |value|
  value.each(&:some_operation)
  OtherModule.finalize! # Side Effect should only happen if there
end                     # are any values

The following ‘and_then` only executes if `value` responds truthy to any?

Maybe([]).continue(&:any?).and_then do |value|
  value.each(&:some_operation)
  OtherModule.finalize!
end

Returns:



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# File 'lib/danom/maybe.rb', line 50

def continue
  and_then do |value|
    value if yield value
  end
end