# C#

---

1. c# 6.0
2. C# 7.0
3. C# 7.1
4. C# 7.2
5. C# 7.3
6. C# 8.0
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## C# 6.0

### Read-only auto-properties enable read-only types

- Creating a public read/write property with a private backing field

class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public DateTime DateOfBirth { get; set; }

}


class Person
{
    public string FirstName { get; private set; }
    public string LastName { get; private set; }
    public DateTime DateOfBirth { get; private set; }

    public Person(string first, string last, DateTime birth)
    {
        this.FirstName = first;
        this.LastName = last;
        this.DateOfBirth = birth;
    }
}

- C# readonly

class Person
{
    public string FirstName { get { return firstName; } }
    private readonly string firstName;
    public string LastName { get { return lastName; } }
    private readonly string lastName;
    public DateTime DateOfBirth { get { return dateOfBirth; } }
    private readonly DateTime dateOfBirth;

    public Person(string first, string last, DateTime birth)
    {
        this.firstName = first;
        this.lastName = last;
        this.dateOfBirth = birth;
    }
}

- C# 6.0
- The backing field can be set through the property name, but only in a constructor.

class Person
{
    public string FirstName { get; }
    public string LastName { get; }
    public DateTime DateOfBirth { get; }

    public Person(string first, string last, DateTime birth)
    {
        this.FirstName = first;
        this.LastName = last;
        this.DateOfBirth = birth;
    }
}

- [Example](https://docs.microsoft.com/en-ca/dotnet/csharp/tutorials/exploration/csharp-6?tutorial-step=1)

---

### Expression-bodied members

public override string ToString()
{
    return FirstName + " " + LastName;
}

public override string ToString() => FirstName + " " + LastName;

### A better string format

---

public override string ToString() => $"{FirstName} {LastName}";

---

### Quick and easy null checks

bool hasMore = s?.ToCharArray()?.GetEnumerator()?.MoveNext() ?? false;

---

### Exception filters

- 連線資料庫

using System;

public class Program
{
    public static void Main()
    {
        try 
        {
            string s = null;
            Console.WriteLine(s.Length);

        } catch (Exception e) when (LogException(e))
        {
        }
        Console.WriteLine("Exception must have been handled");
    }

    private static bool LogException(Exception e)
    {
        Console.WriteLine($"\tIn the log routine. Caught {e.GetType()}");
        Console.WriteLine($"\tMessage: {e.Message}");
        return false;
    }
}

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# nameoF

https://ithelp.ithome.com.tw/articles/10210675

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https://docs.microsoft.com/zh-tw/dotnet/csharp/whats-new/csharp-8

http://www.informit.com/articles/article.aspx?p=2416187

https://docs.microsoft.com/zh-tw/dotnet/csharp/whats-new/csharp-6
---