The Question Mark Operator in Ruby on rails
By: Brian Marick in Ruby Tutorials on 2008-10-17
You'll often find yourself selecting between two alternative values for a variable. That can be done like this:
if input < 0
output = 0
output = input
But it seems wrong to take up five lines for such a simple idea. You can reduce it to two by picking one of the values and then possibly overriding it:
output = input
output = 0 if input < 0
But it's a little confusing for the code to do something and then immediately say, "Wait! I didn't mean that!" So there's a compact version of if for just this purpose:
output = (input < 0) ? 0 : input
You can read that as "if input is less than zero, then return 0, else return whatever object input names."
This ?: construct is called either the question mark operator or, more question mark operator often, the ternary operator. ("Ternary" because it uses three expres- ternary operator sions, unlike operators such as +, which have two and are called binary operators.) binary operators
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