泛型类型的指针？ [英] Pointers of generic type?

问题描述

好的，我想创建一个将改变数据类型值的泛型类。我想这样做的原因是我可以撤消和重做方法。我可以为我需要的每个值类型编写一个类。 I.E. double，int ...但是如果我可以创建一个泛型类来做到这一点会容易得多。

这就是我的

  class CommandChangeDouble：Command 
 {
 double _previous; 
 double _new; 
 double * _objectRef; 
 
 public unsafe CommandChangeDouble（double * o，double to）
 {
 _objectRef = o; 
 _previous = * o; 
 _new = to; 
 * _objectRef = _new; 
} 
 
 public unsafe void void Undo（）
 {
 * _objectRef = _previous; 
} 
 public unsafe void重做（）
 {
 * _objectRef = _new; 
 
 
 $ / code $ / pre 
 
 
这就是我想要的
  class CommandChangeValue< T> ：命令
 {
 T _previous; 
 T _new; 
 T * _objectRef; 
 
 public unsafe CommandChangeValue（T * o，T to）
 {
 _objectRef = o; 
 _previous = * o; 
 _new = to; 
 * _objectRef = _new; 
} 
 
 public unsafe void void Undo（）
 {
 * _objectRef = _previous; 
} 
 public unsafe void重做（）
 {
 * _objectRef = _new; 
 
 
 
 
 
 
 $ b 
但是这给了我错误ErrorCan not take the地址，获取大小或者声明托管类型的指针（'T'）
 
 
 
有没有更好的方法来做到这一点或获取方式围绕这个错误？
解决方案
不是提供一个指向值的指针，而是提供一个setter：
  class CommandChangeValue< T> ：命令
 {
 T _previous; 
 T _new; 
动作< T> _组; 
 
 public CommandChangeValue（T值，Action< T> setValue，T newValue）
 {
 _previous = value; 
 _new = newValue; 
 _set = setValue; 
 setValue（_new）; 
} 
 
 public void Undo（）{_set（_previous）; } 
 public void重做（）{_set（_new）; } 
} 
 
 
 // ... 
 double v = 42; 
 var c = new CommandChangeValue（v，d => v = d，99）; 
  
 
ok so i want to make a generic class that will change the value of a datatype. The reason i want to do this is so i can have undo and redo methods. I could write a class for each valuetype i need. I.E. double, int... but it would be much easier if i could create a generic class to do this.

This is what i have
class CommandChangeDouble : Command
{
    double _previous;
    double _new;
    double* _objectRef;

    public unsafe CommandChangeDouble(double* o, double to)
    {
        _objectRef = o;
        _previous = *o;
        _new = to;
        *_objectRef = _new;
    }

    public unsafe void Undo()
    {
        *_objectRef = _previous;
    }
    public unsafe void Redo()
    {
        *_objectRef = _new;
    }
}
this is what i want
class CommandChangeValue<T> : Command
{
    T _previous;
    T _new;
    T* _objectRef;

    public unsafe CommandChangeValue(T* o, T to)
    {
        _objectRef = o;
        _previous = *o;
        _new = to;
        *_objectRef = _new;
    }

    public unsafe void Undo()
    {
        *_objectRef = _previous;
    }
    public unsafe void Redo()
    {
        *_objectRef = _new;
    }
}
but this gives me the error Error "Cannot take the address of, get the size of, or declare a pointer to a managed type ('T')"

Is there a better way to do this or a way to get around this error?
解决方案
Instead of supplying a pointer to the value, supply a setter:
class CommandChangeValue<T> : Command
{
    T _previous;
    T _new;
    Action<T> _set;

    public CommandChangeValue(T value, Action<T> setValue, T newValue)
    {
        _previous = value;
        _new = newValue;
        _set = setValue;
        setValue(_new);
    }

    public void Undo() { _set(_previous); }
    public void Redo() { _set(_new); }
}


// ...
double v = 42;
var c = new CommandChangeValue(v, d => v = d, 99);


                        
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