Generics

List Type Safety

List<T> stores a collection where every item has the same type.

type safety Type safety catches mismatched values before a program runs.

List Type Safety

extra
ListTypeSafety.cs
Replay: real traced execution (multi-file project)
using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        int extra = 4;
        List<int> scores = new List<int>();
        scores.Add(10);
        scores.Add(extra);

        int total = 0;
        foreach (int score in scores)
        {
            total += score;
        }

        Console.WriteLine($"extra={extra}");
        Console.WriteLine($"count={scores.Count}");
        Console.WriteLine($"total={total}");
    }
}

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        int extra = 1;
        List<int> scores = new List<int>();
        scores.Add(10);
        scores.Add(extra);

        int total = 0;
        foreach (int score in scores)
        {
            total += score;
        }

        Console.WriteLine($"extra={extra}");
        Console.WriteLine($"count={scores.Count}");
        Console.WriteLine($"total={total}");
    }
}

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        int extra = 8;
        List<int> scores = new List<int>();
        scores.Add(10);
        scores.Add(extra);

        int total = 0;
        foreach (int score in scores)
        {
            total += score;
        }

        Console.WriteLine($"extra={extra}");
        Console.WriteLine($"count={scores.Count}");
        Console.WriteLine($"total={total}");
    }
}

  1. extra ← 4, total ← 0

    5{6    static void Main()7    {8        int extra→ 4 = 4; //@extra=1, 89        List<int> scores = new List<int>();10        scores.Add(10);11        scores.Add(extra4);1213        int total→ 0 = 0;14        foreach (int score in scores)

  2. total ← 10

    pass 1 of 2
    13int total = 0;14foreach (int score10 in scores)15{16    total→ 10 += score10;17}

  3. total ← 14

    pass 2 of 2
    13int total = 0;14foreach (int score4 in scores)15{16    total→ 14 += score4;17}

  4. Console.WriteLine($"extra={extra}");

    19    Console.WriteLine($"extra={extra4}");20    Console.WriteLine($"count={scores.Count2}");21    Console.WriteLine($"total={total14}");22}
    outputextra=4
count=2
total=14

  1. extra ← 1, total ← 0

    5{6    static void Main()7    {8        int extra→ 1 = 1;9        List<int> scores = new List<int>();10        scores.Add(10);11        scores.Add(extra1);1213        int total→ 0 = 0;14        foreach (int score in scores)

  2. total ← 10

    pass 1 of 2
    13int total = 0;14foreach (int score10 in scores)15{16    total→ 10 += score10;17}

  3. total ← 11

    pass 2 of 2
    13int total = 0;14foreach (int score1 in scores)15{16    total→ 11 += score1;17}

  4. Console.WriteLine($"extra={extra}");

    19    Console.WriteLine($"extra={extra1}");20    Console.WriteLine($"count={scores.Count2}");21    Console.WriteLine($"total={total11}");22}
    outputextra=1
count=2
total=11

  1. extra ← 8, total ← 0

    5{6    static void Main()7    {8        int extra→ 8 = 8;9        List<int> scores = new List<int>();10        scores.Add(10);11        scores.Add(extra8);1213        int total→ 0 = 0;14        foreach (int score in scores)

  2. total ← 10

    pass 1 of 2
    13int total = 0;14foreach (int score10 in scores)15{16    total→ 10 += score10;17}

  3. total ← 18

    pass 2 of 2
    13int total = 0;14foreach (int score8 in scores)15{16    total→ 18 += score8;17}

  4. Console.WriteLine($"extra={extra}");

    19    Console.WriteLine($"extra={extra8}");20    Console.WriteLine($"count={scores.Count2}");21    Console.WriteLine($"total={total18}");22}
    outputextra=8
count=2
total=18