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and and or

In a comment on Ruby Stylista, I mentioned how I use the and and or keywords in Ruby. To refresh, and and or work just like && and ||, only with very low precedence. For example:

foo = 5 && 10; foo
  => 10
foo = (5 && 10); foo;
  => 10
foo = 5 and 10; foo
  => 5
(foo = 5) and 10; foo
  => 5

You can see from the examples how the expression is 'grouped' by the very low precedence of and and or. Since they have such low precedence, I use them to create conditional execution, to tie two imperative statements together. For example, you could write:

foo = fubar() if do_something()

This reverses the order of execution, putting the clause do_something() after foo = fubar() even though it will happen in the opposite order. If you wish to write them in temporal order, you can use and:

do_something() and foo = fubar()

This puts "first things first." Likewise you can use or to reverse the order of an unless statement. Instead of:

raise 'fubar' unless do_something()

You could write:

do_something() or raise 'fubar'

Again putting the first thing first. I normally only do this if both clauses are imperative. In other words, I would not rewrite either of these statements because the predicate is a query with no side-effects:

foo = fubar() if something.blank?
raise 'fubar' unless something?

The predicate seems less important than the consequent, which suggests that it should come second even though the test is performed first.


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