c# - EqualityComparer.Default 在内部是如何工作的？

Question

考虑 T = 字符串。

我很好奇它是否使用类似这样的东西:typeof(EqualityComparer<T>).GetInterface("IEqualityComparer<T>");

任何建议..

Answer 1

由 Reflector 提供:

public static EqualityComparer<T> Default
{
    get
    {
        EqualityComparer<T> defaultComparer = EqualityComparer<T>.defaultComparer;
        if (defaultComparer == null)
        {
            defaultComparer = EqualityComparer<T>.CreateComparer();
            EqualityComparer<T>.defaultComparer = defaultComparer;
        }
        return defaultComparer;
    }
}

private static EqualityComparer<T> CreateComparer()
{
    RuntimeType c = (RuntimeType) typeof(T);
    if (c == typeof(byte))
    {
        return (EqualityComparer<T>) new ByteEqualityComparer();
    }
    if (typeof(IEquatable<T>).IsAssignableFrom(c))
    {
        return (EqualityComparer<T>) RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType) typeof(GenericEqualityComparer<int>), c);
    }
    if (c.IsGenericType && (c.GetGenericTypeDefinition() == typeof(Nullable<>)))
    {
        RuntimeType type2 = (RuntimeType) c.GetGenericArguments()[0];
        if (typeof(IEquatable<>).MakeGenericType(new Type[] { type2 }).IsAssignableFrom(type2))
        {
            return (EqualityComparer<T>) RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType) typeof(NullableEqualityComparer<int>), type2);
        }
    }
    if (c.IsEnum && (Enum.GetUnderlyingType(c) == typeof(int)))
    {
        return (EqualityComparer<T>) RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType) typeof(EnumEqualityComparer<int>), c);
    }
    return new ObjectEqualityComparer<T>();
}

所以你可以看到如果 T = string 它将返回 GenericEqualityComparer<string> .