In the code below, if I replace the and in the any? statement with &&, it throws an error unexpected tIDENTIFIER, expecting '}'.
def ArrayAddition(arr)
i = 2
until i == arr.length
combinations = arr.permutation(i).to_a
return true if combinations.any?{|array| array.inject(&:+) == arr.max and !array.include? arr.max}
i+=1
end
false
end
What is going on here? Does Ruby handle these operators differently?
Yes. and has lower precedence than && (and almost everything else). This expression:
foo and bar baz
...is parsed like this:
foo and (bar baz)
...so Ruby knows foo is a method name (because it can't be anything else). On the other hand, this expression:
foo && bar baz
...is parsed like this:
(foo && bar) baz
...which just doesn't make sense and you get a syntax error.
Generally speaking you should use && unless you specifically want and's lower precedence, so in this case the easiest fix to the syntax error is to use parentheses around the method argument:
foo && bar(baz)
...and so:
array.inject(&:+) == arr.max && !array.include?(arr.max)
As a bonus, this is more readable as well.
The operators and and && have different precedence, and are not equivalent. As such, the Ruby Style Guide advises against using and and or operators: The and and or keywords are banned. It's just not worth it. Always use && and || instead.
Due to the difference in precedence, the other operators in the expression have higher or lower comparative precedence. In this case, the argument for the Array#include? call end up binding to the wrong expression.
You can solve this by adding parentheses around the argument to the Array#include? call.
