Gwater17 Gwater17 - 1 year ago 88
Ruby Question

Converting array using procs and symbols

I'm working my way through Ruby's Codecademy course and I'm up to here

The correct code (that I don't understand) to convert the array of numbers into an array of strings is posted below.

numbers_array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

strings_array =

I've been looking through the forums and googling and at this point I'm still confused what the heck is going on in this code.

I'm confused by
means to convert to strings and
stands for symbols. Does
convert stuff into symbols or strings?

I'm confused by
too. I get that the
sign makes the block that follows it into a proc, but here it's the colon for symbol and the method to convert to a string rather than a block that follows the

I'd really appreciate any help!

Answer Source

What happens is that the syntax &:to_s is another way constructing a block that calls the method that matches the symbol, on every item in the array. In your case, it is basically the same as writing:

strings_array = { |number| number.to_s }

Here is another example:

strings_array =
# Same as
strings_array = { |number| number.to_f }

For further explanation regarding the & sign, look at how you would define a method that accepts a block as an argument.

def map(&block)
  # ....

Now look at the different ways we could invoke this method that all will yield the same result.

# Block using bracket notation
map { |n| n.to_i }

# Block using do ... end notition
map do |n|

# When using ampersand, ruby will try to treat the following as a 
# proc and use to proc as the block for the method. If we pass a proc
# to it, then no problem.
p = proc { |n| n.to_i }

# When using ampersand with a symbol (or any other non-proc objects), 
# ruby will try to call the to_proc method on the object and use that
# as a block. And in the scenario of passing a symbol, the Symbol 
# object will return a proc that calls the method that matches the symbol.
:to_i.to_proc => #<Proc:...>
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