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[??] [Treehouse]

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In this badge, we're going to be talking about Ruby Core.

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Ruby Core is a collection of classes and modules that come with your Ruby installation.

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So let's get started.

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Now we're going to take a look at symbols in Ruby.

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Symbols in Ruby are very similar to strings.

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However, one of the big differences is that symbols only exist in memory

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once during a session in Ruby.

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Let's take a look at how that works.

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Go ahead and launch IRB right now.

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I'm going to create a hash called treehouse.

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At first, I'm going to use strings for hash keys.

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Now we have our treehouse hash.

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If we wanted to redo this hash using symbols instead of using quotes,

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we would use a colon.

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Let's see what that looks like.

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Now we have basically the same thing as our first hash.

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However, our hash keys are symbols.

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The difference is if we made another hash--let's say called treehouse2--

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the Ruby interpreter would not create new objects each time.

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In the first version where we use strings,

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each time we initialize a hash key, a new string object is created.

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However, when we use symbols, we're always referring to the same symbol.

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And there are a couple of different ways of creating hash keys as symbols as well.

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In newer versions of Ruby, from 1.9.2 and up,

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you don't have to put a colon in front of the symbol

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in order to denote it as a hash key.

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And we can see that that produces the same symbols as before.

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Now let's see how we might use this in one of our Ruby programs.

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I'm going to put all of these examples in a directory called core.

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Now let's create a very simple class called BankAccount

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and show how to use symbols.

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In our deposit method, we're going to use an options hash.

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The options hash is going to have a default value

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that's going to let us add a memo to our deposit.

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So what we'll do is conditionally assign the memo to the phrase "Regular deposit."

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Then we're going to add on to these transactions.

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Now we can go ahead and instantiate our bank account.

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Now when we call the deposit method, we can pass in an amount.

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If we don't pass in a memo, it will just add the default memo.

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Let's go ahead and call deposit again,

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but this time we'll send in a memo as well.

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And just for fun, let's see what our bank account looks like.

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Let's go ahead and run this program and see what happens.

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And we can see that in our transactions array

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at first we got the memo of "Regular deposit,"

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and in the second transaction we had the memo "This was a gift."

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Each time, the amount and memo symbols are not recreated.

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They're referencing the same symbol in memory.

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And finally, one reason that you might use symbols

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is because if you're going to define a method name,

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you can use a symbol.

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By defining a method, the symbol will exist in memory anyway.

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And that's how you work with symbols in Ruby.

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In our next video, we're going to be working with dates and times.

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[??] [Treehouse]