无参数方法在OOP中是邪恶的，这是如何对待它的方法

你好！

这个想法是在不可变对象中的任何地方都使用惰性缓存的属性，在这种情况下，我们通常会使用没有参数的处理器密集型方法。以及文章-如何设计它以及为什么。

可视地访问对象的惰性属性

TL； DR位于最底部。

为什么邪恶？

. , Integer, :

public sealed record Integer(int Value);

Value int. , :

public sealed record Integer(int Value)
{
    public Integer Triple() => new Integer(Value * 3);
}

, , . ,

public int SomeMethod(Integer number)
{
    var tripled = number.Triple();
    if (tripled.Value > 5)
        return tripled.Value;
    else
        return 1;
}

,

public int SomeMethod(Integer number)
    => number.Tripled > 5 ? number.Tripled.Value : 1;

, , , . , , Tripled .

?

1. . , , .
2. . , , ( — ).
3. . immutable object, , Equals GetHashCode , - , .

, , . , :

public sealed record Number(int Value)
{
    public int Number Tripled => tripled.GetValue(@this => new Number(@this.Value * 3), @this);
    private FieldCache<Number> tripled;
}

:

1 ( ?):

public sealed record Number(int Value)
{
    public int Number Tripled => new Number(@this.Value * 3);
}

( )

2 ( Lazy<T>):

public sealed record Number : IEquatable<Number>
{
    public int Value { get; init; }  //   ,   
    public int Number Tripled => tripled.Value;
    private Lazy<Number> tripled;
    public Number(int value)
    {
        Value = value;
        tripled = new(() => value * 3);  //        ,      this-   
    }

    //   Equals,    ,    ,    Lazy<T>  
    public bool Equals(Number number) => Value == number.Value;
    //     GetHashCode
    public override int GetHashCode() => Value.GetHashCode();
}

, . , ? , .

, with, , (-). Lazy, .

3 ( ConditionalWeakTable):

public sealed record Number
{
    public Number Tripled => tripled.GetValue(this, @this => new Integer(@this.Value * 3));
    private static ConditionalWeakTable<Number, Number> tripled = new();
}

. ValueType ConditionalWeakTable -. , - ( , , 6 , , ).

4 ( ):

public sealed record Number
{
    public int Value { get; init; }

    public Number Tripled { get; }
    public Number(int value)
    {
        Value = value;
        Tripled = new Number { Value = value * 3 };
    }
}

stackoverflow, , "" — , .

1. , , . ?
2. Equals GetHashCode true 0 . , , . , Equals GetHashCode , .
3. . , , .
4. , GetValue, , ConditionalWeakTable. -, Lazy<T>.
5. with, initialized holder, — .

!

, :

public struct FieldCache<T> : IEquatable<FieldCache<T>>
{
    private T value;
    private object holder; //       ,    generic 
    //    , ,   Equals     
    public bool Equals(FieldCache<T> _) => true;
    public override int GetHashCode() => 0;
}

GetValue :

public struct FieldCache<T> : IEquatable<FieldCache<T>>
{
        public T GetValue<TThis>(Func<TThis, T> factory, TThis @this) where TThis : class // record -   .   ,    
        {
            //        (,   - null)
            if (!ReferenceEquals(@this, holder))
                lock (@this)
                {
                    if (!ReferenceEquals(@this, holder))
                    {
                        //    ,    FieldCache   ,  -         . , ,     ,      
                        value = factory(@this);
                        holder = @this;
                    }
                }
            return value;
        }
}

, :

public sealed record Number(int Value)
{
    public int Number Tripled => tripled.GetValue(@this => new Number(@this.Value * 3), @this);
    private FieldCache<Number> tripled;
}

, .

, , FieldCache — Lazy<T>.

BenchFunction — - , , . . , FieldCache<T> , Lazy<T>.

, , , .

TL;DR

: , .

而且，众所周知，现有的方法不允许做得精美，因此您必须编写自己的方法。