类型参数约束 - 没有泛型（或最近的提议！） [英] Type Parameter Constraints - no generics (or nearest offer!)

问题描述

我想我想做的是不可能的，但我想我会问。我想在不同的指标测量之间实现某种自定义转换 - 例如将英寸转换为米和其他单位。

I am thinking what I want to do is impossible but thought I would ask anyway. I am thinking of implementing some kind of custom conversion between different metric measurements - such as converting inches to metres and other units.

我认为基本类称为Unit如下。注意：我没有在任何字段中保存单位数，例如2米，5英寸等：

I am thinking base class called Unit as follows. NOTE: I have not put in any fields to hold the number of units eg 2 metres, 5 inches and so on:

public abstract class Unit {
    protected string _name;
    public Unit(string name)
    {
        _name = name;
    }
}

然后是Meter和Inch的Unit子类： p>

Then subclasses of Unit for Metre and Inch:

public class Metre : Unit {
    public Metre() : base("Metre")
    {
    }
}

public class Inch : Unit {
    public Metre() : base("Inch")
    {
    }
}

我想有一个类，可以处理这些单位之间的转换。例如：

I would like to have a class that could handle conversion of these units between one another. Something like:

public static class UnitConvertor
{
    public Unit Convert(Unit from, Type to) : where Type extends/inherits from Unit
    {
        // do the conversion
        return the instance of Type to;
    }
}

有任何想法吗？

推荐答案

如果提前提前知道单位，您可以使用隐式转换运算子：

If the units are all known ahead of time you could use an implicit conversion operator:

public class Metre : Unit 
{
    public Metre() : base("Metre")
    {
    }

    public static implicit operator Inch(Metre m)  
    { 
        return new Inch(39.37 * m.Value);
    }
}

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