Beginning programmer here, just wanting to understand the process behind Ruby's sort method when using the spaceship operator <=>. Hope someone can help.
In the following:
array = [1, 2, 3]
array.sort { |a, b| a <=> b }
... I understand that sort is comparing a pair of numbers at a time and then returning -1 if a belongs before b, 0 if they're equal, or 1 if a should follow b.
But in the case of sorting in descending order, like so:
array.sort { |a, b| b <=> a }
... what exactly is happening? Does sort still compare a <=> b and then flip the result? Or is it interpreting the returns of -1, 0 and 1 with reversed behavior?
In other words, why does placing the variables in the block like so:
array.sort { |b, a| b <=> a }
...result in the same sorting pattern as in the first example?
a <=> b will return -1 if a belongs before b, 0 if they're equal, or 1 if a should follow b.
b <=> a will return -1 if b belongs before a, 0 if they're equal, or 1 if b should follow a.
Since you are reversing the order, the output should be reversed, just like the - operator, for example. 3-5 is -2, and 5-3 is 2.
array.sort { |b, a| b <=> a } is equal to array.sort { |a, b| a <=> b } because the first argument is before the spaceship, and the second is after. Ruby doesn't care what the name of the variable is.