Generics

Generic Constraints

A generic constraint requires a type parameter to provide certain members.

constraint A constraint limits which types can be used with a generic method or class.

Generic Constraints

name
GenericConstraints.cs
Replay: real traced execution (multi-file project)
using System;

interface INamed
{
    string Name { get; }
}

class Customer : INamed
{
    public string Name { get; }

    public Customer(string name)
    {
        Name = name;
    }
}

class Program
{
    static string Label<T>(T item) where T : INamed
    {
        return "name:" + item.Name;
    }

    static void Main()
    {
        string name = "Mira";
        Customer customer = new Customer(name);
        string label = Label(customer);

        Console.WriteLine($"name={name}");
        Console.WriteLine($"label={label}");
    }
}

using System;

interface INamed
{
    string Name { get; }
}

class Customer : INamed
{
    public string Name { get; }

    public Customer(string name)
    {
        Name = name;
    }
}

class Program
{
    static string Label<T>(T item) where T : INamed
    {
        return "name:" + item.Name;
    }

    static void Main()
    {
        string name = "Noah";
        Customer customer = new Customer(name);
        string label = Label(customer);

        Console.WriteLine($"name={name}");
        Console.WriteLine($"label={label}");
    }
}

using System;

interface INamed
{
    string Name { get; }
}

class Customer : INamed
{
    public string Name { get; }

    public Customer(string name)
    {
        Name = name;
    }
}

class Program
{
    static string Label<T>(T item) where T : INamed
    {
        return "name:" + item.Name;
    }

    static void Main()
    {
        string name = "Zoe";
        Customer customer = new Customer(name);
        string label = Label(customer);

        Console.WriteLine($"name={name}");
        Console.WriteLine($"label={label}");
    }
}

  1. name ← Mira

    25static void Main()26{27    string name→ Mira = "Mira"; //@name="Noah", "Zoe"28    Customer customer = new Customer(name);29    string label = Label(customer);

  2. public Customer(string name)

    12public Customer(string nameMira)13{14    Name = nameMira;15}

  3. customer ← Customer

    27string name = "Mira"; //@name="Noah", "Zoe"28Customer customer→ Customer = new Customer(name);29string label = Label(customerCustomer);

  4. static string Label<T>(T item) where T : INamed

    19{20    static string Label<T>(T itemCustomer) where T : INamed21    {22        return "name:" + item.NameMira;23    }

  5. label ← name:Mira

    28    Customer customer = new Customer(name);29    string label→ name:Mira = Label(customerCustomer);3031    Console.WriteLine($"name={nameMira}");32    Console.WriteLine($"label={labelname:Mira}");33}
    outputname=Mira
label=name:Mira

  1. name ← Noah

    25static void Main()26{27    string name→ Noah = "Noah";28    Customer customer = new Customer(name);29    string label = Label(customer);

  2. public Customer(string name)

    12public Customer(string nameNoah)13{14    Name = nameNoah;15}

  3. customer ← Customer

    27string name = "Noah";28Customer customer→ Customer = new Customer(name);29string label = Label(customerCustomer);

  4. static string Label<T>(T item) where T : INamed

    19{20    static string Label<T>(T itemCustomer) where T : INamed21    {22        return "name:" + item.NameNoah;23    }

  5. label ← name:Noah

    28    Customer customer = new Customer(name);29    string label→ name:Noah = Label(customerCustomer);3031    Console.WriteLine($"name={nameNoah}");32    Console.WriteLine($"label={labelname:Noah}");33}
    outputname=Noah
label=name:Noah

  1. name ← Zoe

    25static void Main()26{27    string name→ Zoe = "Zoe";28    Customer customer = new Customer(name);29    string label = Label(customer);

  2. public Customer(string name)

    12public Customer(string nameZoe)13{14    Name = nameZoe;15}

  3. customer ← Customer

    27string name = "Zoe";28Customer customer→ Customer = new Customer(name);29string label = Label(customerCustomer);

  4. static string Label<T>(T item) where T : INamed

    19{20    static string Label<T>(T itemCustomer) where T : INamed21    {22        return "name:" + item.NameZoe;23    }

  5. label ← name:Zoe

    28    Customer customer = new Customer(name);29    string label→ name:Zoe = Label(customerCustomer);3031    Console.WriteLine($"name={nameZoe}");32    Console.WriteLine($"label={labelname:Zoe}");33}
    outputname=Zoe
label=name:Zoe