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Revision as of 20:24, 9 February 2016
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Ruby Flow Control | Ruby While and Until Loops |
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In this chapter of Ruby Essentials we will look at implementing flow control logic in Ruby scripts through the use of the Ruby case statement.
Ruby Flow Control
In the previous chapter we looked at some basic conditional structures using the if ... else and if .. elsif ... mechanisms. These approaches to building conditional logic work well if you need to check a value against only a few different criteria (for example checking the value of a string against a couple of possible candidates):
if customerName == "Fred" print "Hello Fred!" elsif customerName == "John" print "Hello John!" elsif customername == "Robert" print "Hello Bob!" end
result = case value
when match1 then result1
when match2 then result2
when match3 then result3
when match4 then result4
when match5 then result5
when match6 then result6
else result7
end
There can be any number of when statements - basically as many as you need to fully compare the value in the case statement against the possible options (represented by match1 through to match7 in the above example) specified by the when statements. When a match is found the result is assigned to the optional result variable.
Finally, the else statement specifies the default result to be returned if no match is found.
This concept is, perhaps, best explained using an example. The following Ruby case statement is designed to match a particular car model with a manufacturer. Once a match is found, the car and associated manufacturer are included in an output string:
car = "Patriot" manufacturer = case car when "Focus" then "Ford" when "Navigator" then "Lincoln" when "Camry" then "Toyota" when "Civic" then "Honda" when "Patriot" then "Jeep" when "Jetta" then "VW" when "Ceyene" then "Porsche" when "Outback" then "Subaru" when "520i" then "BMW" when "Tundra" then "Nissan" else "Unknown" end puts "The " + car + " is made by " + manufacturer
When executed, the resulting output will read:
The Patriot is made by Jeep
If no match was found in the case statement, then the default result, defined by the else statement would cause the following output to be generated:
The Prius is made by Unknown
Number Ranges and the case statement
The case statement is also particularly useful when used in conjunction with number ranges (for details of ranges read the Ruby Ranges chapter of this book).
The following case example detects where a number falls amongst a group of different ranges:
score = 70 result = case score when 0..40 then "Fail" when 41..60 then "Pass" when 61..70 then "Pass with Merit" when 71..100 then "Pass with Distinction" else "Invalid Score" end puts result
The above code, when executed will result in a "Pass with Merit" message.
Summary
The if .. else ... approach to building conditional logic into an application works fine for evaluating a limited number of possible criteria. For much larger evaluations, the Ruby case statement is a less cumbersome alternative. In the chapter we have looked at the case statement and reviewed some examples using strings and number ranges.
Purchase and download the full PDF and ePub editions of this Ruby eBook for only $8.99 |
Previous | Table of Contents | Next |
Ruby Flow Control | Ruby While and Until Loops |