Examples of compiling extension methods for abstraction at a higher level than specific types

For a type, if we do not want to or cannot change it, but want to add a method for this type, we can use the extension method. If this type has a higher level of abstraction, such as an interface, we should compile an extension method for a higher level type. In addition, the extension method is the premise of chain programming.

 

Determine whether a set contains elements

List<int> list = new List<int>();if(list != null && list.Count > 0){    }

We can write an extension method for the ICollection interface at a higher level than the int type:

public static bool HasElements(this ICollection list){    return list != null && list.Count > 0}

Then you can use it like this:

List<int> list = new List<int>();if(list.HasElements()){    }

 

Determines whether a value is between two decimal places.

public class A : IComparable{}public class B : IComparable{}public class C : IComparable{}public bool IsBetween(A a, B b, C c){    return a.CompareTo(b) >=0 && c.CompareTo(c) <= 0;}

We can write an extension method for the IComparable interface higher than a specific class:

public static bool IsBetween<T>(this T value, T min, T max) where T : IComparable<T>{    return value.CompareTo(min) >= 0 && value.CompareTo(max) <= 0;}

It can be used as follows:

int a = 10;a.IsBetween(1,8);

 

Implement the same method for each element in the Set

List<string> strList = new List<string>();foreach(var item in strList){    SomeMethod(item);}

First, you can write extension methods for icollections that are more abstract than string. Second, the methods executed by traversal elements are abstracted into a delegate parameter. As follows:

public static void EachMethod<T>(this ICollection<T> items, Action<T> action){    foreach(T item in items)    {        action(item);    }}

You can use the following code:

List<string> strList = new List<string>();strList.EachMethod(s => {    Console.WriteLine(s);});

 

Determine whether an element is included in a collection

string str = "a";List<string> strs = new List<string>(){"a", "b"};if(strs.Contains(str)){    //TODO:}

You can write extension methods for generic types that are more abstract than string:

public static bool In<T>(this T source, params T[] list){    if(source == null) throw new ArgumentNulllException("source");    return list.Contains(source);}

This method is used as follows:

string temp = "a";temp.In("a","b");