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Now, in the last lesson, we created what's called a getter,
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so a block of code that will execute whenever we try to get the value of a property. Now, computed properties
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also allow you to specify some code that should be executed when its value is set
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and this is called a setter.
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So, for example, in addition to this block for "get." underneath it. I can also write a block that's called
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"set," and the block of code inside the set will be executed whenever this property gets a new value set
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to it.
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So, for example, inside here, I can simply write a print statement that says "numberOfSlices
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now has a new value which is,"
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and there's a special variable that we can tap into which is called newValue, and this new value is
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equal to, essentially, exactly that, it's the newValue that's been given to numberOfSlices.
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So, for example, if we delete all of this and we simply write numberOfSlices is equal to 12, then you
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can see right away down here, we get printed numberOfSlices
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now has a new value which is 12, and that new value comes from this line here.
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So having this block of code, which we call the setter, allows us to tap into the exact moment when our property
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is set with a new value, and it allows us to use that new value in computations or various bits of code,
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and to execute it at the exact time when this property's value gets updated.
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Now, if you don't have a setter specified for your computed property, say, if we delete that block, you can
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see that you get an error here
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when I try to set a numberOfSlices equal to 12, and it says that "Cannot assign to value: 'numberOfSlices' is
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a get-only property."
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So because I only have a block specified for "get,"
then this computed property is now effectively read-only,
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so I cannot set it to have a new value, but I can use it whenever I need to.
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So this still works.