Chain of resp. pattern

The Chain of Responsibility pattern provides a chain of loosely coupled objects one of which can satisfy a request. This pattern is essentially a linear search for an object that can handle a particular request.

An example of a chain-of-responsibility is event-bubbling in which an event propagates through a series of nested controls one of which may choose to handle the event.

Chain of resp. dofactory – link
Class code: chain of resp. demo in JAVA!

in – parameter modifier

The in keyword causes arguments to be passed by reference. It makes the formal parameter an alias for the argument, which must be a variable. In other words, any operation on the parameter is made on the argument. It is like the ref or out keywords, except that in arguments cannot be modified by the called method. Whereas ref arguments may be modified, out arguments must be modified by the called method, and those modifications are observable in the calling context.

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Class code: in example

Mutable vs. Immutable

Mutable and immutable are English words that mean “can change” and “cannot change” respectively. The meaning of these words is the same in C# programming language; that means the mutable types are those whose data members can be changed after the instance is created but Immutable types are those whose data members can not be changed after the instance is created.

When we change the value of mutable objects, value is changed in same memory. But in immutable type, the new memory is created and the modified value is stored in new memory.

Let’s start with examples of predefined classes (String and StringBuilder)

StringBuilder in C#

A String is immutable, meaning String cannot be changed once created. For example, new string “Hello World!!” will occupy a memory space on the heap. Now, by changing the initial string “Hello World!!” to “Hello World!! from Tutorials Teacher” will create a new string object on the memory heap instead of modifying the initial string at the same memory address. This behaviour will hinder the performance if the same string changes multiple times by replacing, appending, removing or inserting new strings in the initial string.

To solve this problem, C# introduced StringBuilder. StringBuilder is a dynamic object that allows you to expand the number of characters in the string. It doesn’t create a new object in the memory but dynamically expands memory to accommodate the modified string

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Structs in C#

Structs share most of the same syntax as classes. The name of the struct must be a valid C# identifier name. Structs are more limited than classes in the following ways:

• Within a struct declaration, fields cannot be initialized unless they are declared as const or static.
• A struct cannot declare a parameterless constructor (a constructor without parameters) or a finalizer.
• Structs are copied on assignment. When a struct is assigned to a new variable, all the data is copied, and any modification to the new copy does not change the data for the original copy. This is important to remember when working with collections of value types such as Dictionary<string, myStruct>.
• Structs are value types, unlike classes, which are reference types.
• Unlike classes, structs can be instantiated without using a new operator.
• Structs can declare constructors that have parameters.
• A struct cannot inherit from another struct or class, and it cannot be the base of a class. All structs inherit directly from ValueType, which inherits from Object.
• A struct can implement interfaces.
• A struct cannot be null, and a struct variable cannot be assigned null unless the variable is declared as a nullable value type.

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Class code: Struct example

Value Types in C#

Value types and reference types are the two main categories of C# types. A variable of a value type contains an instance of the type. This differs from a variable of a reference type, which contains a reference to an instance of the type. By default, on assignment, passing an argument to a method, or returning a method result, variable values are copied. In the case of value-type variables, the corresponding type instances are copied

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More topics covered:

• Structs GetHasCode
• Structs Equals
• Structs boxing/unboxing

Links:

• Eclipse – download link
• Structs – tutorials teacher link
• Lesson Summary Video!