我如何创建一个使用整数的类型，至少支持加法减法除法和乘法以及保证和整数数字IF如果操作导致整数（否则抛出）。
例如，我希望能够做到这样的事情：
Precise A = 10;
A.Divide(3);
A.GetNumber(); // This would throw an exception as 10/3 isn't an int.
A.Multiply(6);
int result = A.GetNumber; // I want result to be = to 20, not to a floating point type that would round to 2 or be very close like 1.9999999999999999999999998992
我意识到这是一个奇怪的用例，但我确实有这个需要（执行一系列操作，浮点数可以错过，但保证最终成为有效的int）。
答案 0 :(得分：5)
因为我们无法知道10 / 3最终会产生一个精确的整数答案，直到* 6我们不得不推迟到那时为止：
public sealed class Precise
{
private interface IOperation
{
int Calculate(int value);
IOperation Combine(IOperation next);
}
private sealed class NoOp : IOperation
{
public static NoOp Instance = new NoOp();
public int Calculate(int value)
{
return value;
}
public IOperation Combine(IOperation next)
{
return next;
}
}
private sealed class Combo : IOperation
{
private readonly IOperation _first;
private readonly IOperation _second;
public Combo(IOperation first, IOperation second)
{
_first = first;
_second = second;
}
public int Calculate(int value)
{
return _second.Calculate(_first.Calculate(value));
}
public IOperation Combine(IOperation next)
{
return new Combo(_first, _second.Combine(next));
}
}
private sealed class Mult : IOperation
{
private readonly int _multiplicand;
public Mult(int multiplicand)
{
_multiplicand = multiplicand;
}
public int Calculate(int value)
{
return value * _multiplicand;
}
public int Multiplicand
{
get { return _multiplicand; }
}
public IOperation Combine(IOperation next)
{
var nextMult = next as Mult;
if(nextMult != null)
return new Mult(_multiplicand * nextMult._multiplicand);
var nextDiv = next as Div;
if(nextDiv != null)
{
int divisor = nextDiv.Divisor;
if(divisor == _multiplicand)
return NoOp.Instance;//multiplcation by 1
if(divisor > _multiplicand)
{
if(divisor % _multiplicand == 0)
return new Div(divisor / _multiplicand);
}
if(_multiplicand % divisor == 0)
return new Mult(_multiplicand / divisor);
}
return new Combo(this, next);
}
}
private sealed class Div : IOperation
{
private readonly int _divisor;
public Div(int divisor)
{
_divisor = divisor;
}
public int Divisor
{
get { return _divisor; }
}
public int Calculate(int value)
{
int ret = value / _divisor;
if(value != ret * _divisor)
throw new InvalidOperationException("Imprecise division");
return ret;
}
public IOperation Combine(IOperation next)
{
var nextDiv = next as Div;
if(nextDiv != null)
return new Div(_divisor * nextDiv._divisor);
var nextMult = next as Mult;
if(nextMult != null)
{
var multiplicand = nextMult.Multiplicand;
if(multiplicand == _divisor)
return NoOp.Instance;
if(multiplicand > _divisor)
{
if(multiplicand % _divisor == 0)
return new Mult(multiplicand / _divisor);
}
else if(_divisor % multiplicand == 0)
return new Div(multiplicand / _divisor);
}
return new Combo(this, next);
}
}
private sealed class Plus : IOperation
{
private readonly int _addend;
public Plus(int addend)
{
_addend = addend;
}
public int Calculate(int value)
{
return value + _addend;
}
public IOperation Combine(IOperation next)
{
var nextPlus = next as Plus;
if(nextPlus != null)
{
int newAdd = _addend + nextPlus._addend;
return newAdd == 0 ? (IOperation)NoOp.Instance : new Plus(newAdd);
}
return new Combo(this, next);
}
}
private readonly int _value;
private readonly IOperation _operation;
public static readonly Precise Zero = new Precise(0);
private Precise(int value, IOperation operation)
{
_value = value;
_operation = operation;
}
public Precise(int value)
: this(value, NoOp.Instance)
{
}
public int GetNumber()
{
return _operation.Calculate(_value);
}
public static explicit operator int(Precise value)
{
return value.GetNumber();
}
public static implicit operator Precise(int value)
{
return new Precise(value);
}
public override string ToString()
{
return GetNumber().ToString();
}
public Precise Multiply(int multiplicand)
{
if(multiplicand == 0)
return Zero;
return new Precise(_value, _operation.Combine(new Mult(multiplicand)));
}
public static Precise operator * (Precise precise, int value)
{
return precise.Multiply(value);
}
public Precise Divide(int divisor)
{
return new Precise(_value, _operation.Combine(new Div(divisor)));
}
public static Precise operator / (Precise precise, int value)
{
return precise.Divide(value);
}
public Precise Add(int addend)
{
return new Precise(_value, _operation.Combine(new Plus(addend)));
}
public Precise Subtract(int minuend)
{
return Add(-minuend);
}
public static Precise operator + (Precise precise, int value)
{
return precise.Add(value);
}
public static Precise operator - (Precise precise, int value)
{
return precise.Subtract(value);
}
}
这里每个Precise都有一个整数值和一个将在其上执行的操作。进一步的操作会产生一个新的Precise（做一个像mutable一样疯狂的事情），但是如果可能的话，这些操作会组合成一个更简单的操作。因此＆＃34;除以3然后乘以6＆＃34;变为＆＃34;乘以2＆＃34;。
我们可以这样测试：
public static void Main(string[] args)
{
Precise A = 10;
A /= 3;
try
{
var test = (int)A;
}
catch(InvalidOperationException)
{
Console.Error.WriteLine("Invalid operation attempted");
}
A *= 6;
int result = (int)A;
Console.WriteLine(result);
// Let's do 10 / 5 * 2 = 4 because it works but can't be pre-combined:
Console.WriteLine(new Precise(10) / 5 * 2);
// Let's do 10 / 5 * 2 - 6 + 4 == 2 to mix in addition and subtraction:
Console.WriteLine(new Precise(10) / 5 * 2 - 6 + 4);
Console.Read();
}
一个好的解决方案也可以很好地处理LHS为整数且RHS为Precise并且其中Precise;留给读者的练习;）
遗憾的是，我们必须处理(10 / 3 + 1) * 3更加复杂，必须在Combine实施中进行改进。
编辑：进一步研究上述问题以便至少捕获大部分边缘情况，我认为它应该从仅处理两个Precise对象之间的操作开始，因为要{ {1}} - ＆gt; int是微不足道的，很容易被放在首位，但是Precise - ＆gt; Precise需要调用计算，可能为时过早。我还使操作成为关键的操作（操作存储一个或两个对象，而这些对象又包含操作或值）。然后，如果您开始使用总和int的表示并将其乘以6，则更容易将其转换为(10 / 3) + 5，在最终计算时可以给出精确的结果(10 * (6 / 3)) + (5 * 6)而不是因为它击中了不精确的50。
答案 1 :(得分：1)
如果你不允许任意精确的合理性，那么你似乎在没有更多约束的情况下问不可能。
取1并将其除以65537两次，然后乘以65537两次以检索1：这不能适合32位整数。
答案 2 :(得分：0)
然后使用Math.Round（）进行最终答案。
答案 3 :(得分：0)
我会使用小数作为操作结果，并在.ToString上使用GetNumber检查是否有＆＃34;。＆＃34;如果是，我抛出异常，如果不是，我将它转换为int。