Why do I get the following error:
irb >> x == "AN" && arr.include? ("bar")
SyntaxError: (irb):80: syntax error, unexpected tLPAREN_ARG, expecting $end
x == "AN" && arr.include? ("bar")
^
But this works fine:
x == "AN" && (arr.include? ("bar"))
It looks to be doing this: ( x == "AN" && arr.include? ) && ("bar"). What the ambiguity here?
You shouldn't be spacing out your arguments, it leads to confusing interpretations:
x == "AN" && arr.include?("bar")
The ambiguity is in trying to determine if ("bar") is an argument or something else.
There are occasions where you can get away with the space, but it's generally a habit you don't want to get into.
&& has a very strong precedence therefore irb is parsing it as:
x == ("AN" && arr.include?) ("bar")
# Syntax error
leading to the error (especially because of the space between include? and ().
You may want to use parenthesis to ensure the correct order for the evaluation:
(x == "AN") && arr.include?("bar")
# true / false
In this case you can also use and:
x == "AN" and arr.include? ("bar")
# false / true
which have a lower precedence.
&& to and. The code would be clearer with the additional parenthesis.
and has been built exactly for this type of situations. Using too many parenthesis can be messy.
and was build for such situations. I think it is best practice to use && for boolean expression and and for control flow. Some people think you should never use and and or (github.com/styleguide/ruby).