How does Array#sort work when a block is passed?

Question

I am having a problem understanding how array.sort{ |x,y| block } works exactly, hence how to use it?

An example from Ruby documentation:

Answer 1

In:

a.sort {|x,y| y <=> x }   #=> ["e", "d", "c", "b", "a"]

what is x and y?

x and y are the elements being compared by the sorting algorithm.

This is useful to define for custom classes which element should be before the other.

For basic data ( numbers, strings , date, etc ) the natural order is predefined, but for customer element ( ie Employee ) you define who goes before who in a comparison. This block give you the chance to define that.

and what happens at y<=>x?

There, they are comparing the elements in descending order ( those with "higher" value will go first ) rather than the natural order ( x<=>y )

The <=> method stands for "compareTo" and return 0 if the elements are equivalent, or < 0 if x goes before than y or > 0 if x goes after y