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Hello.
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In this video, we're going to talk about question 5: "What are expression-bodied members?" 
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Expression-bodied members of a type
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are members define which expression body instead of regular body with braces.
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These sounds are very cryptic, but in practice, it's quite simple, and it allows us to write very concise
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and readable code.
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Let's see expression-bodied members in practice.
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Here is the Person class.
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Let's focus on the ToString method.
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This is a regular method and its body is contained in braces.
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Simple as it is, it takes quite a lot of space.
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While actually only this part is really defining the logic of this method.
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This part contains a single expression.
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But first, what is an expression?
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And the expression is a piece of code that evaluates to some value.
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This is an expression that for the Person with Name John and YearOfBirth 1972 will evaluate to string
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"John who was born in 1972".
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If a method contains only a single expression, it can be defined as an expression-bodied method.
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Let's try this with the ToString method.
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Let's see what happened.
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First of all, I removed the braces that typically surround the body of the method.
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I also removed the "return" keyword and simply placed what this method returns to the right side of
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the arrow operator.
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And that's it.
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This method does exactly the same thing as before, and it only takes a single line of code.
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So the general blueprint for expression-bodied methods is this.
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We define the return type and the name of the method on the left side of the arrow. On the right side
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we define an expression whose value will be returned.
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Expression-bodied methods are short and readable.
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Their limitation is that they must only contain a single expression.
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So, for example, this method could not be changed to an expression-bodied method.
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This method contains more than one expression, as well as several statements.
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A statement is a piece of code that does something but does not evaluate to a value.
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For example, Console.Writeline calls are statements.
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If a method contains a single statement, it can also be changed to a void expression-bodied method.
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Let's see this in practice.
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This method simply prints the information about the person to the console.
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It doesn't return anything as its return type is void.
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All right.
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We learned about the expression-bodied methods, but there are more expression-bodied members we
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can have.
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One of the most common use cases for them is a read-only property.
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Let's define an Age property, which will return the current year minus the year of birth of the person.
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Again, this is extremely simple code, but it takes seven lines.
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Let's change it to an expression-bodied read-only property.
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Great.
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No, it only takes a single line of code.
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The property doesn't need to be read-only to be defined with expression body.
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Let's add the LastName property to the Person class.
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Last names can be changed, most often when someone gets married.
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So let's enable the modification of this property.
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This is how the properties looked like before C# 3. For your information in this course
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we are using C# 10, so you can guess C# 3 was quite some time ago. Starting with C# 4
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the auto-implemented properties were introduced, allowing us to write code like this.
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This was a huge improvement.
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And it still works great in the 99 percent of the cases.
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But sometimes we want to execute some additional operations during getting and setting of the backing
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field.
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For example, we may want to trim the whitespace characters when setting the last name property.
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In this case, we're not able to use the auto-implemented property because it simply assigns the value
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on set without any additional operations.
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So we are stuck with implementing the getter and setter ourselves.
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Let's do it now.
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This will work, but it still takes a tremendous amount of space.
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Let's change this property to an expression-bodied property.
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And here it is, only 5 lines instead 11. Another thing I wanted to talk about is expression-bodied
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constructor.
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The problem with it is that it allows only a single operation to be executed, which here is not the
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case.
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We assign both name and year of birth in the constructor, but for the sake of the example, let me
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define a second constructor which only assigns the name.
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As you can see, it's also a nice one-liner, so it may be still a good idea to use it if we only execute
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a single operation in the constructor.
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We can also define expression-bodied destructive.
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Let's add a destructor to this class.
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The last members that can be defined with expression body are indexer, but we'll talk more about
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them later in the course.
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Let's summarize. Expression-bodiedmembers of a type
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are members defined with expression body instead of the regular body with braces. To define them, we
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must use the arrow operator. Expression-bodied members allow us to make the code much shorter.
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During the interview, you may hear questions like "What is an expression?"
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Expression is a piece of code that evaluates to some value.
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For example, two plus five evaluates to seven.
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"What is a statement?"
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A statement is a piece of code that does something, but it doesn't evaluate one value.
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For example, calling the Console.Writeline method is a statement.
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It does not evaluate any value as the Console.Writeline method is void.
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All right, that's it about the expression-bodied members. Thanks for watching, and I'll see you
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in the next lecture.