This community-built FAQ covers the “Symbols, Meet Procs” exercise from the lesson “Blocks, Procs, and Lambdas”.
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This exercise can be found in the following Codecademy content:
Learn Ruby
FAQs on the exercise Symbols, Meet Procs
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I’m curious about why we need to add the colon : to do the conversion successfully.
strings_array = numbers_array.collect(&:to_s)
My reading of the code above is: Ruby first has to turn to_s into a symbol and then turns it into a proc, so that the .collect method can use it legally
Is my reading correct? If it is, why do we need to turn it into a symbol first? Why can’t we just write the piece as below?
strings_array = numbers_array.collect(&to_s)
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I also wished there had been more explanation on this exercise
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Why does the colon need to be there? Why are we turning to_s into a symbol?
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Does anyone know why the following code doesn’t work?
numbers_array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers_array.each { |n| puts n.to_s }
It returns a list of integers anyway
Does it mean that .to_i, .to_str and other converting commands work only with .collect and .map?
The codeacademy lesson is pretty thin on the explanation. I found this to be a very good explanation: https://www.brianstorti.com/understanding-ruby-idiom-map-with-symbol/
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https://www.codecademy.com/courses/learn-ruby/lessons/blocks-procs-and-lambdas/exercises/symbols-meet-procs
you can also convert symbols to procs using that handy little &.
Earlier, we were told that procs are actually converted to blocks using ‘&’, as the methods require a block rather than a proc. So, I am wondering if preceding a symbol with an ‘&’ does not rather convert them to a block rather than a proc.
The way that I understood it is this:
Symbols are used 1. as hash keys and 2. to reference method names.
Since to_s is a method, I read it as using :to_s to reference that method, and then & to turn it into a block so that .collect could use it.
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That code doesn’t work because it doesn’t create the array strings_array from the array numbers_array, plus it doesn’t make use of the ‘Symbol#to_proc’ syntax which is the point of the exercise.
What #each does is that it calls the given block once for each element in self, passing that element as a parameter. It returns the array itself (thus: numbers_array)
#=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
whereas the instructions tell us to create a strings_array that should be the string version of the corresponding element from the numbers_array, returning:
#=> ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]
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