3. Classes, Records, Structs, and Tuples

Question 1

What does ‘pass by value’ mean?

Answer 1

The actual value of the first variable is copied to the second variable.

Question 2

What does ‘pass by reference’ mean?

Answer 2

With a reference type the variable holds only the memory location where the object is storied (unlike a value type where the variable holds the actual value). So, when you use the reference variable in code, the variable tells the code where the object is located (unlike a value type which would all give the actual value to the code).

If you copy reference value A to reference value B, only the memory location of what A is pointing to is copied to B. Which means, both A and B now point to the same object.

Question 3

Where is a reference type variable storied in memory? And where is a value type variable normally storied in memory?

Answer 3

• The reference type variable is storied in the heap.
• The value type variable is normal storied in the stack.

Question 4

What is boxing? What is unboxing?

Answer 4

Boxing is when a value type (also known as a struct) is wrapped inside a reference type and is storied, along with that reference type, inside the heap.

Unbox is when that value type is unwrapped from that reference type and placed back into the stack.

Question 5

A record type, created with the record keyword, is considered a value or reference type.

Answer 5

It is a reference type.

(Obviously, an object can be of more than one type. Here a record type is a record, but it is also a reference type.)

Question 6

What is ‘syntax sugar’?

Answer 6

It is a slang term meaning the something that simply makes coding easier without adding any new fuctionality.

Question 7

Is a tuple a value type or reference type?

Answer 7

Strangely (I think), it is a value type.

Because behind the scenes it uses a struct type, which is a value type.

Question 8

What is the key difference between a static member of a class and an instance member?

Answer 8

An instant of a class is a specific implementation of a class. A single class might have many different implementations. The non-static members of each implementation would be independently of the non-static members in other implementations (they can have different values).

But not the static members. The static member of one implementation is the same as the static members of other implementation (meaning, if they have variables, those variables will always be same for all the implementaions).

This is perhaps a bit confusing, but not too hard once you start doing examples.

Question 9

What is the keyword for creating a static member in a class?

Answer 9

The keyword is: static.

Question 10

List all the kinds of members a class can have (there are at least eleven)?

Answer 10

(In no particular order of importance because they are all important)

1. Fields
2. Constants
3. Methods
4. Properties
5. Constructors
6. Indexers
7. Operators
8. Events
9. Destructors
10. Deconstructors
11. Types

Question 11

What is a field?

Answer 11

A field is a variable normally placed at the very top of a class (not inside a method or other member).

Question 12

What does the readonly keyword do for a field?

Answer 12

It assures the field’s value can only be changed in the constructor. Once the constructor has ran, and the value of the field is set, the field’s value can no longer be changed.

Question 13

What is the purpose of a property?

Answer 13

A property has the same purpose as a field; it creates a variable that can be used throughout the class. But a property can contain programming code that will limit the values the property can have.

For example, a variable for a person’s age should not allow for negative ages or ages of large numbers, say over 120 or so.

Question 14

What are a ‘get’ and a ‘set’?

Answer 14

They are the important part of a property.

• A ‘get’ retrieves the value of the property.
• A ‘set’ can set the value of a property.

Question 15

Can a property’s get and set have different access levels?

Answer 15

Yes.

Question 16

Does a property have to have both a get and a set?

Answer 16

No.

You can leave out either the get or the set. By omitting the set, you make the property read only.

Question 17

How can you constrain a property so its value can only be set in the constructor or with an object initializer?

Answer 17

By using the init keyword instead of the set keyword.

Question 18

What is a function?

Answer 18

It is not synonymous with a method.

A function includes other members such as indexers, operators, constructors, destructors, and properties. As well as methods.

Question 19

What are the parts that make up a method?

Answer 19

• Method modifiers (such a public or static).
• The return type (if nothing is returned it would be ‘void’).
• The name of the method.
• Enclosed in parenthese will be the list of parameters the methods nees to operate.
• Finally, comes the main body of the method that is enclosed in curly brackets { } .
• Within the curly brackets are all the code the method requires.

Question 20

What are the parts that make up the parameters that go into between the parentheses of a method?

Answer 20

• The paramter type (int, float, string, etc).
• And the parameter name which is used to access the parameter.
• The coma used to separate two are more paramters.
• And other modifiers such as params, in, ref, out.

Question 21

What is an expression-bodied method?

Answer 21

It’s a simplified way of writing a method. But,

• The method must have only one statement.
• The curly brackets and return keyword are not needed.
• Use the => operator to separate the left fro right side.

Question 22

Identify the type of statement for each bolded line below:

public class Math
{
**public int Value { get; set; }
 public int GetSquare() =\> Value \* Value;
 public static int GetSquareOf(int x) =\> x \* x;**
}

Answer 22

• public int Value { get; set; } is a property
• public int GetSquare() => Value * Value; an expression-bodied method that is not static
• public static int GetSquareOf(int x) => x * x; an expression-bodied method that is static.

Question 23

What is meant by a method’s signature?

Answer 23

The signature of a method is its name and the number of parameters it has and the types of signatures it has.

A single method can have many variations, meaning that they all have the same name, but the number and types of parameters will differ. This is overloading.

Question 24

Name two things not sufficient to create an overloaded method.

Answer 24

• Different return types.
• Parameters with different names.

Meaning, you cannot overload a method simply by giving it a different return type or by giving the parameters different names.

Question 25

What is a name argument?

Answer 25

All (I think they all do) parameters have names. But when invoking a method you do not need to use those names when supplying arguments because is you place the argument in the propert order the method knows which parameter they belong to.

However, you can, if you want, use the parameter name when supplying arguments. This is optional and can make your code easier to read.

Question 26

What makes an argument optional?

Answer 26

If it has a default value.

When the parameters of a method are defined, if those parameters are give default values then the parameter is optional.

Question 27

Can you define more than one optional parameters for a method?

Answer 27

Yes, you can define as many as you need.

Question 28

What is the purpose of the params keyword?

Answer 28

Easier to show than explain, but I’ll try explaining anyway. The params keyword is always place before the definition of an array type. For example:

public void AnyNumberOfArguments(params int[] data)
{
foreach (var x in data)
{
Console.WriteLine(x);
}
}

(The array type can be any type.)

But when this method is being used, an unlimited number of items (this this example of type int) can be placed as arguments. The compiler will group all the items into an array.

Question 29

What is a constructor?

Answer 29

Every class has a constructor. If you do not create one yourself, the compiler will create one.

A constructor is a special method that gets the class started. It will make sure all the basic stuff that needs to be done to make the class work gets done. For example it will make sure all fields are initialized to default values.

A constructor has the same name as the class and it has no return type.

Question 30

Can constructors be overloaded?

Answer 30

Yes, they can. And it is very common that they will be.

An overloaded constructor means you have multiple constructors defined, each with the same name, but each have a unique number and types of parameters. (They must each have a different signature.)

Question 31

When does the compiler create a default constructor?

Answer 31

When you do not create one.

Question 32

Does a constructor require an access modifier?

Answer 32

In almost all cases the answer is yes. To make your class work as expected you will need to add the ‘public’ access modifier.

You can use other access modifiers, such as private or protected, but this would not be normal and you need to understand what your doing and why your doing it.

Question 33

When can a constructor be implementated as a expression body?

Answer 33

The term ‘expression body’ make this sound much harder than it is.

If the constructor will consist of just one line, instead writing a bunch of curly braces, you can use the => symbol.

Question 34

What should you do if you have multiple constructor overloads and they have code in common?

Answer 34

You should not duplicate the same code in each constructor.

Instead, you should involk a constructor that has the code from the second construtor using the the this keyword.

Question 35

Does it ever make sense to have static constructors?

Answer 35

Yes, it often makes very good sense.

Static members of a class can be used even if the class has not been initialized (using the ‘new’ keyword). The static constructor will assure that the static methods are initialized correctly before being used.

Question 36

How often and when will a static constructor be involked?

Answer 36

Just once.

It will run before any other part of the class is ran.

Question 37

What is a local function?

Answer 37

It’s basically a method inside another method.

Question 38

What are some important restrictions to know about local functions?

Answer 38

• The local function can only be accessed by the method it is inside.
• Parameters and return types are used in the same way as normal methods.
• A local function can be implementated with an expression-body or by using the curly brackets.
• A local method can be static.

Question 39

What are extension methods?

Answer 39

They are static methods that extend other types. Extension methods make use of the ‘this’ keyword.

Question 40

What is an anonymous type?

Answer 40

It’s a type without a name. It makes use of the ‘var’ and ‘new’ keywords.

Question 41

How do you create an anonymous type?

Answer 41

Start with the ‘var’ keyword,

Add a name,

the ‘=’ sign

use the ‘new’ keywords,

and the two curly brackets { },

put something between the curly brackets { }.

Question 42

What are ‘records’?

Answer 42

They are reference types that support value semantics.

Question 43

What is the purpose of ‘records’?

Answer 43

To reduce the amount of code you have to write.

Question 44

Are ‘records’ immutable or mutable?

Answer 44

Trick question. They are both.

Question 45

What are the two kinds of ‘records’?

Answer 45

• Nominal records
• Positional records

Question 46

What makes a “nominal record” different from an object using the ‘class’ keyword?

Answer 46

A ‘record’ can contain all the members of a class. The difference is that a record has some added or different functionality.

Question 47

What makes ‘positional records’ different from ‘nominal records’?

Answer 47

They are mostly the same, but ‘positional records’:

• Have parentheses after the name of the record to specific the members of the record.
• Have additional methods for deconstruction.

Question 48

How does equality comparison with records work?

Answer 48

To understand this, you need to understand the difference between how reference types and value types handle equality.

With reference types, equality compares memory locations. If two reference variables point to the same memory location, then they would equate to true.

For value types it is the actual value of the variable that matters, not memory locations. I variable A is 7 and variable B is also 7, the equality comparison would be true (regardless of where they are stored in memory).

With ‘record types’ this is flipped. A record type is also a reference type, but it compares values like a value type.