Ruby: Conditional Matrix? Case with Multiple Conditions

Ruby: conditional matrix? case with multiple conditions?

Boolean case (with no expression in the case, it returns the first branch with a truthy when_expr):

result = case
when A && B then ...
when A && !B then ...
when !A && B then ...
when !A && !B then ...
end

Matching case (with an expression in the case, it returns the first branch that satisfies the predicate when_expr === case_expr):

result = case [A, B]
when [true, true] then ...
when [true, false] then ...
when [false, true] then ...
when [false, false] then ...
end

Ruby: Two conditions in Case statement

The conditions in a case statement are not Boolean expressions; they are values that are compared against the target object using the === operator. Of course, any class can override that operator, but the predefined one only returns true for a small set of conditions (like is_a?, equals, is contained in, =~...). Having a Boolean expression as the when condition doesn't trigger a match when that expression is true; it triggers a match when the target object === the value of the expression, and for most objects, obj === true is not itself true.

So you might want to swap out your case for an if/else chain in this instance:

if a.is_a? String
  puts 'string'
elsif a.is_a?(Array) && a.all? { |obj| obj.is_a? String }
  puts 'an array with only string classes'
else
  raise ArgumentError, "unsupported object #{a}:#{a.class}"
end

Or do a nested check inside the case condition. But then you would have two else states, one for the if (meaning it matched the array case but wasn't all strings) and one for the case (meaning it was something else entirely). So rather than duplicate the error-handling code like that, I used a boolean variable to indicate when an error needed to be raised:

ok = false
case a
 when String
  puts 'string'
  ok = true
 when Array
  if a.all? { |obj| obj.is_a? String }
    puts 'an array with only string classes'
    ok = true
  end
end
if !ok 
  raise ArgumentError, "unsupported object #{a}:#{a.class}"
end

How does a ruby case statement with multiple conditions work

If you want the exact substitute of if-elsif functionality, you should use empty case condition:

case
when @mails_hash.include?(mail) && @mails_hash[mail] > 0
  p "true"
  true
when @mails_hash.include?(mail) && @mails_hash[mail] == 0
  @mails_hash[mail] =+ 1
  p "false double"
  false
else
  p "false else"
  false
end

When you put an argument in call to case, it’s used to compare against when clauses using threeequals aka case-equal:

case mail
when MailClass then ...
end

The code above actually calls MailClass.===(mail).

Multiple conditions in if statement Ruby

Following line looks wrong,

array[4][4].include?(mark) &&

Remove &&

Ruby if statement multiple conditions not equal

I think what you are trying to achieve, can be done by-

H.each do |key, v|
  if (key != "a") && (key != "b")
    puts key
  end
end

Note - || operator will return true if any of the two conditions is true.

Hope that helps.

How do I write a complex multi-line if condition in Ruby?

The short answer is the operator needs to be at the end of the line in order to tell Ruby to continue reading the next line as part of the statement, so this would work:

if ( (aa != nil && self.prop1 == aa.decrypt) ||
   (bb != nil && self.prop2 == bb.decrypt) ) &&
   (self.id.nil? || self.id != id)
  return true
end

That being said, you can probably reduce the logic by throwing exceptions based on input values, and removing some redundant checks (I'm making some jumps here about what your variables will look like, but you get the idea.)

raise 'aa must support decrypt' unless aa.respond_to? :decrypt
raise 'bb must support decrypt' unless bb.respond_to? :decrypt
if prop1 == aa.decrypt || prop2 == bb.decrypt
  if self.id != id
    return true
  end
end

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