Understanding map in Ruby

Question

I'm pretty new to Ruby and am trying to understand an example of the map method that I came across:

{:a => "foo", :b => "bar"}.map{|a, b| "#{a}=#{b}"}.join('&')

which returns:

=> "a=foo&b=bar"

I don't understand how the

b=bar

is returned. The string interpolation is what is confusing me as it seems it would return something like:

=> "a=foo&bbar"

Answer 1

> {:a => "foo", :b => "bar"}.map{|key, value| "#{key}=#{value}"}
#=> ["a=foo", "b=bar"]

map method will fetch each element of hash as key and value pair

"#{key}=#{value}" is a String Interpolation which adds = between your key and value

Using this syntax everything between the opening #{ and closing } bits is evaluated as Ruby code, and the result of this evaluation will be embedded into the string surrounding it.

Array#join will returns a string created by converting each element of the array to a string, separated by the given separator.

so here in your case:

> ["a=foo", "b=bar"].join('&')
#=> "a=foo&b=bar" 

---

In Rails you can convert hash to query params using Hash#to_query method, which will return the same result.

 > {:a => "foo", :b => "bar"}.to_query
 #=> "a=foo&b=bar"