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Hello.

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In this video, we're going to talk about Topic 19.

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What is pattern matching?

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Pattern matching is a technique where you test an expression to determine if it has certain characteristics.

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The easiest way to understand popular matching is with an example.

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Let's say I want to run some code if some value is no and other if it isn't.

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This code is pretty straightforward.

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There is only one problem.

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We don't know what this object is exactly, and it may turn out that it is some type of quality operator

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of an old and that it actually does something else than simply taking if the value is new.

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To avoid this, we can use our first pattern from pattern matching the nortec pattern.

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Well, it's not rocket science.

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This pattern just works if an object is known, but pattern matching can give us much, much more ability.

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Let's walk through some more complex examples.

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One of the most commonly used buttons is type test.

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I want to run some code if a variable is of some type.

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Moreover, if it is, I want to cast it to this type.

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We felt pattern matching.

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I would need to write something like this.

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Here I am talking.

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If the object is strong, I could do it even simpler by using the East Keyword, which we learned about

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before.

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So first, I'd check if the object is trying, and then I passed it to string with pattern matching.

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I can do it all in one line.

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This is quite convenient.

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These are string variable will be available only if this object is a string.

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So I would not be able to use it anywhere else than inside this if statement.

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We can also object some particular properties of the target object.

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Here we checked if an object is a pet with weight larger than 10000 and put equal to fish.

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All right, the next type of pattern matching is comparing discrete values.

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This is very similar to using plain old sweet statement.

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Here I have a method.

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Taking a string that should represent a number and another string saying what type of number it is.

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So, for example, int decimal or float, depending on the second parameter.

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I want to convert the first parameter to the given type.

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Let's do it with pattern matching.

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Please notice this special case.

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This is a discard pattern, and it works similarly as default in this which statement.

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It will be executed if the type parameter is not equal to any of the specified values.

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Let's get two more complex types of pattern matching.

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The next one is a relational pattern.

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It allows us to check how a given value compares two constants.

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As you can see, called, using pattern matching is very simple and readable.

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The cool thing about pattern matching is that it has very good visual studio and compiler support.

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And we get an error when we do something silly.

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For example, let me add some more cases here.

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This code doesn't compile because the last two cases are unreachable.

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The cases are executed from top to bottom.

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So when the eight parameter S10 will hit, the less than 20 case will never reach the less than 11 case.

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So what we should do is fix the order of the cases.

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Right now, this will work as expected.

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This code actually demonstrates one more pattern, no logical pattern.

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We used it here.

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Where we checked it out is less than 20 and more than 60.

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We can also use pattern matching quilted construction.

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What we learned about before.

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As you can see, we deconstructed the object into its components, and we used them to define a pretty

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complex logic.

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We could all meet the parameter names.

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But personally, I would rather leave them for readability.

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As you can see, this also works.

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We can also mix the construction with taking particular properties.

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All right.

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So we learned some of the most basic usages of pattern matching.

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There is also a question when to use them and when to use plain old if and switch statements.

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In my opinion, you should simply use those that you find more reliable.

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You can also mix both to get what's best in any of them.

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To summarize, pattern matching is a technique where you can test an expression to determine if it has

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certain characteristics.

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During the interview, you can be asked about one of the most popular patterns.

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How can we check if an object is of a given type and customized to this type in the same line?

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For that, we can use pattern matching.

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For example, we could write if Param is string text.

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This way will cost the around to the string variable called text, but only if this object is of type

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strength.

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All right.

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That's it for this lecture.

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Thanks for watching, and I'll see you in the next one.