奇怪的是，我一直认为我们应该始终将高机会子句放在嵌套 if-else 的前面，直到今天。
简要设置：
一个数组Zoo[]包含 5 个类别的 10,000 个对象，基于权重，例如 4,3,2,1,0（表示 4000 只猫、3000 只狗、2000 只鸡、1000 只兔子、0 只猫头鹰），它可以被洗牌或不洗牌（完全按顺序）。
然后使用if-else检查每个数组成员。
结果：时间（毫秒）
Weights 43210 01234 22222 43210 01234 22222
Shuffle Yes Yes Yes No No No
Polymorphism 101 100 107 26 26 27
If Else 77 28 59 17 16 17
If Else Reverse 28 77 59 16 17 16
Switch 21 21 21 18 19 18
当我看到If-Else反面比if-else. 这里if-else检查 Cat->Dog->Chicken->Rabbit->Owl，反向版本以相反的顺序检查它们。
另外，有人可以在非随机版本中解释每种方法都有很大的改进吗？（我会假设由于缓存或内存中更好的命中率？）
更新
Weights 27 9 3 1 0 0 1 3 9 27 27 9 3 1 0 0 1 3 9 27
Shuffle Yes Yes No No
Polymorphism 84 82 27 27
If Else 61 20 17 16
If Else Reverse 20 60 16 17
Switch 21 21 18 18
代码如下：
class Animal : AnimalAction
{
public virtual int Bart { get; private set; }
public int Type { get; private set; }
public Animal(int animalType)
{
this.Type = animalType;
}
}
interface AnimalAction
{
int Bart { get; }
}
class Cat : Animal
{
public Cat()
: base(0)
{
}
public override int Bart
{
get
{
return 0;
}
}
}
class Dog : Animal
{
public Dog()
: base(1)
{
}
public override int Bart
{
get
{
return 1;
}
}
}
class Chicken : Animal
{
public Chicken()
: base(2)
{
}
public override int Bart
{
get
{
return 2;
}
}
}
class Rabbit : Animal
{
public Rabbit()
: base(3)
{
}
public override int Bart
{
get
{
return 3;
}
}
}
class Owl : Animal
{
public Owl()
: base(4)
{
}
public override int Bart
{
get
{
return 4;
}
}
}
class SingleDispatch
{
readonly Animal[] Zoo;
int totalSession;
SingleDispatch(int totalSession, int zooSize)
{
this.totalSession = totalSession;
Zoo = new Animal[zooSize];
int[] weights = new int[5] { 0, 1, 2, 3, 4 };
int totalWeights = weights.Sum();
int[] tiers = new int[4];
int accumulated = 0;
for (int i = 0; i < 4; i++)
{
accumulated += weights[i] * zooSize / totalWeights;
tiers[i] = accumulated;
}
for (int i = 0; i < tiers[0]; i++)
{
Animal nextAnimal = new Cat();
Zoo[i] = nextAnimal;
}
for (int i = tiers[0]; i < tiers[1]; i++)
{
Animal nextAnimal = new Dog();
Zoo[i] = nextAnimal;
}
for (int i = tiers[1]; i < tiers[2]; i++)
{
Animal nextAnimal = new Chicken();
Zoo[i] = nextAnimal;
}
for (int i = tiers[2]; i < tiers[3]; i++)
{
Animal nextAnimal = new Rabbit();
Zoo[i] = nextAnimal;
}
for (int i = tiers[3]; i < zooSize; i++)
{
Animal nextAnimal = new Owl();
Zoo[i] = nextAnimal;
}
Zoo.FisherYatesShuffle();
}
public static void Benchmark()
{
List<Tuple<string, double>> result = new List<Tuple<string, double>>();
SingleDispatch myBenchmark = new SingleDispatch(1000, 10000);
result.Add(TestContainer.RunTests(10, myBenchmark.SubClassPoly));
result.Add(TestContainer.RunTests(10, myBenchmark.Ifelse));
result.Add(TestContainer.RunTests(10, myBenchmark.IfelseReverse));
result.Add(TestContainer.RunTests(10, myBenchmark.Switch));
foreach (var item in result)
{
Console.WriteLine("{0,-30}{1:N0}", item.Item1, item.Item2);
}
Console.WriteLine();
}
void SubClassPoly()
{
long sum = 0;
for (int i = 0; i < totalSession; i++)
{
foreach (var myAnimal in Zoo)
{
sum += myAnimal.Bart;
}
}
}
void Ifelse()
{
long sum = 0;
for (int i = 0; i < totalSession; i++)
{
foreach (var myAnimal in Zoo)
{
if (myAnimal.Type == 0)
{
sum += 0;
}
else if (myAnimal.Type == 1)
{
sum += 1;
}
else if (myAnimal.Type == 2)
{
sum += 2;
}
else if (myAnimal.Type == 3)
{
sum += 3;
}
else
{
sum += 4;
}
}
}
}
void IfelseReverse()
{
long sum = 0;
for (int i = 0; i < totalSession; i++)
{
foreach (var myAnimal in Zoo)
{
if (myAnimal.Type == 4)
{
sum += 4;
}
else if (myAnimal.Type == 3)
{
sum += 3;
}
else if (myAnimal.Type == 2)
{
sum += 2;
}
else if (myAnimal.Type == 1)
{
sum += 1;
}
else
{
sum += 0;
}
}
}
}
void Switch()
{
long sum = 0;
for (int i = 0; i < totalSession; i++)
{
foreach (var myAnimal in Zoo)
{
switch (myAnimal.Type)
{
case 0:
sum += 0;
break;
case 1:
sum += 1;
break;
case 2:
sum += 2;
break;
case 3:
sum += 3;
break;
case 4:
sum += 4;
break;
default:
break;
}
}
}
}
}