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Skip named parameter

I have a structure that takes 3 named parameters in a constructor ...

public struct MyData
{
    private readonly double _value1;
    private readonly double _value2;
    private readonly double _value3;

    public MyData(
        double value1 = 1.0,
        double value2 = 2.0,
        double value3 = 3.0)
    {
        _value1 = value1;
        _value2 = value2;
        _value3 = value3;
    }
}

A call to the method that the class creates gets in the three valid doubling values ​​that I want to use to create the MyData class only if the zero number doubles not equal ...

public MyData CreateMyData(double? value1, double? value2, double? value3)
{
    MyData myData;
    if (value1.HasValue)
    {
        if (value2.HasValue)
        {
            if (value3.HasValue)
            {
                myData = new MyData(value1, value2, value3); 
            }
            else
            {
                myData = new MyData(value1, value2); 
            }
        }
        else
        {
            if (value3.HasValue)
            {
                myData = new MyData(value1, value3: value3); 
            }
            else
            {
                myData = new MyData(value1); 
            }
        }
    }
    else
    {
        if (value2.HasValue)
        {
            if (value3.HasValue)
            {
                myData = new MyData(value2: value2, value3: value3); 
            }
            else
            {
                myData = new MyData(value2: value2); 
            }
        }
        else
        {
            if (value3.HasValue)
            {
                myData = new MyData(value3: value3); 
            }
            else
            {
                myData = new MyData(); 
            }
        }
    }
    return myData;
}

Is there a better way to write this method without changing the MyData class? That is, is it possible to conditionally pass named parameters, or can I pass an indicator to represent the default values ​​by default?

+3
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5 answers
public MyData(
    double? value1 = null,
    double? value2 = null,
    double? value3 = null)
{
    _value1 = value1 ?? 1.0;
    _value2 = value2 ?? 2.0;
    _value3 = value3 ?? 3.0;
}

Thus, you can transmit nulldirectly and not suffer from a Raman explosion .

, - , .

+2

   public  MyData CreateMyData(double? value1, double? value2, double? value3)
    {
        var ss= typeof(MyData).GetConstructor(new Type[]{typeof(double),typeof(double),typeof(double)});
        var parametesr = ss.GetParameters();
        return new MyData(value1 ?? Convert.ToDouble(parametesr[0].DefaultValue), value2 ?? Convert.ToDouble(parametesr[1].DefaultValue), value3 ?? Convert.ToDouble(parametesr[2].DefaultValue)); 
    }
+1

Perhaps you just want to:

return new MyData(value1 ?? 1.0, value2 ?? 2.0, value3 ?? 3.0);

?

0
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var t = typeof (MyData);
var c = t.GetConstructor(new Type[] { typeof(double), typeof(double), typeof(double)});
var p = c.GetParameters();
return new MyData(value1 ?? p[0].DefaultValue, value2 ?? p[1].DefaultValue, value3 ?? p[2].DefaultValue);
0
source

For this you need late binding. The open source framework ImpromptuInterface gives you access to the DLR functions needed to dynamically select named arguments .

using ImpromptuInterface;

...

public MyData CreateMyData(double? value1, double? value2, double? value3)
{
    var arg = InvokeArg.Create;
    var argList = new List<Object>();
    if(value1.HasValue)
        argList.Add(arg("value1",value1));
    if(value2.HasValue)
        argList.Add(arg("value2",value2));
    if(value3.HasValue)
        argList.Add(arg("value3",value3));

    return Impromptu.InvokeConstructor(typeof(MyData), argList.ToArray());
}
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