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rubyclassconditional-operator
Jae Song
Jae Song

Reputation: 21

Ruby - Question Mark usage in Class Method

I'm having a little difficulty in understanding the below under initialize, and color methods. This is from the solution I was given:

The one under initialize: I think it means @given equals value, and if value is equal to 0, then its false, otherwise its true

Under color not sure what the 2nd question mark means.

def initialize(value)
  @value = value
  @given = value == 0 ? false : true
end

def color
  given? ? :blue : :red
end

def given?
  @given
end

Upvotes: 2

Views: 69

Answers (2)

Syed Samiuzzaman
Syed Samiuzzaman

Reputation: 136

Mostly we use ? mark as a part of the method's name which returns boolean value. this is just a convention we ruby coders use to follow.

In your example given? is the method name as it return boolean value so here we have follow the convention.

and in ternary conditional operator we use

condition ? do something when condition is true : do something when condition is false

In your case given? it's returning true or false and which is also method name

So the first question mark is a part of the method name and 2nd question mark is the part of ternary condition

Upvotes: 1

Jörg W Mittag
Jörg W Mittag

Reputation: 369623

Under color not sure what the 2nd question mark means.

This is called the conditional operator. (See, for example, section 11.5.2.2.5 Conditional operator expression of the ISO Ruby Language Specification.)

condition ? consequence_truthy : consequence_falsy

will evaluate condition and depending on whether the result is truthy or falsy, it will evaluate either the first or the second consequence.

Personally, I find the conditional operator useless in Ruby. In C and similar languages, the conditional operator is required because it is an expression, whereas the conditional statement is, well, a statement. So, if you need to use a conditional in an expression, you cannot use a conditional statement, you must use the conditional operator.

However, this does not apply to Ruby: in Ruby, everything is already an expression, there are no statements. The conditional expressions (see, for example, section 11.5.2.2.2 The if expression, section 11.5.2.2.3 The unless expression, and section 11.5.2.2.4 The case expression) can already be used as an expression, so there is no need to use the conditional operator.

Personally, I find the conditional expression more readable than the conditional operator:

if condition then consequence_truthy else consequence_falsy end

This is semantically equivalent to the conditional operator, the only difference is syntactical: it has different precedence, which however, actually works more natural than the precedence of the conditional operator.

So, your examples could, in my opinion, be clearer written as

def initialize(value)
  @value = value
  @given = if value == 0 then false else true end
end

def color
  if given? then :blue else :red end
end

Actually, the initialize contains a useless-use-of-conditional because Integer#== already returns a boolean. So, the following would be even clearer:

def initialize(value)
  @value = value
  @given = value != 0
end

Upvotes: 3

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