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NOTE You already know that local variables must start with a lowercase letter and can t contain any characters other than letters, numbers, and underscores. Method names are restricted to the same rules, which means they often look like variables. Keywords (like if, or, when, and, and others) share the same set of properties. How does the Ruby interpreter know the difference When Ruby encounters a word, it sees it as a local variable name, a method invocation, or a keyword. If it s a keyword, then Ruby knows it and responds accordingly. If there's an equals sign (=) to the right of the word, Ruby assumes it s a local variable being assigned. If it s neither a keyword nor an assignment, Ruby assumes it s a method being invoked and sends the method to the implied receiver, self.

Note Notice that you don t need to restart the web server when you make changes to your project files.

Don t worry if this code seems confusing and unfamiliar, as we ll be covering this type of technique more in the following chapters. Do note, however, the style used in the final puts statements. It s easy to manipulate dates with these helpers! The Time class also allows you to create Time objects based on arbitrary dates: Time.local(year, month, day, hour, min, sec, msec) The preceding code creates a Time object based on the current (local) time zone. All arguments from month onward are optional and take default values of 1 or 0. You can specify months numerically (between 1 and 12), or as three-letter abbreviations of their English names. Time.gm(year, month, day, hour, min, sec, msec)

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Ch apt er 3 rUB Y S B U IL DING B L OC K S : Da t a , e X p r e S S I O N S , a N D F LO W C O N t r O L

We ll go through all the specifics of model validations in 5. For now, we re using only the most primitive methods of protecting our data. It shouldn t surprise you that Active Record is capable of much more involved validations, such as making sure that a numeric value was entered, validating that data is in the correct format using regular expressions, and ensuring unique values, among other checks.

Ruby is an object-oriented (OO) programming language. If you ve never worked in an OO language before, the metaphors used can be confusing the first time you hear them. Basically, objects are simple ways to separate your code and the data it contains. Let s say you re writing a program to help track the athletic program at a school. You have a list of all the students who are currently participating on a team, along with their student IDs. This example looks at the rowing team. You could keep an array of arrays representing the students on the team: rowing_team = [[1975, "Smith", "John"], [1964, "Brown", "Dan"], ...] This is an array of [id, first_name, last_name]. You d probably need to add a comment to explain that. If you wanted multiple teams, you could wrap this in a hash: teams = { :rowing => [[1975, "Smith", "John"], [1964, "Brown", "Dan"], ...], :track => [[1975, "Smith", "John"], [1900, "Mark", "Twain"], ...] } That works for now. But it s kind of ugly, and you could easily get confused, especially if you kept adding teams. This style of coding is referred to as procedural, and it s not object-oriented. You re keeping track of huge data collections that are made up of simple types. Wouldn t it be nice to keep all this data more organized

The preceding code creates a Time object based on GMT/UTC. Argument requirements are the same as for Time.local. Time.utc(year, month, day, hour, min, sec, msec) The preceding code is identical to Time.gm, although some might prefer this method s name. You can also convert Time objects to an integer representing the number of seconds since the UNIX time epoch: Time.gm(2007, 05).to_i

Note Regular expressions (regex for short) are expressions that describe patterns in strings. They are

1177977600 Likewise, you can convert epoch times back into Time objects. This technique can be useful if you want to store times and dates in a file or a format where only a single integer is needed, rather than an entire Time object: epoch_time = Time.gm(2007, 5).to_i t = Time.at(epoch_time) puts t.year, t.month, t.day

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