Passing an empty array as default value of an optional parameter [duplicate]

问题:

This question already has an answer here:

• Setting the default value of a C# Optional Parameter 3 answers

How does one define a function that takes an optional array with an empty array as default?

public void DoSomething(int index, ushort[] array = new ushort[] {},  bool thirdParam = true) 

results in:

Default parameter value for 'array' must be a compile-time constant.

回答1:

You can't create compile-time constants of object references.

The only valid compile-time constant you can use is null, so change your code to this:

public void DoSomething(int index, ushort[] array = null,   bool thirdParam = true) 

And inside your method do this:

array = array ?? new ushort[0]; 

回答2:

If you can make the array the last argument you could also do this:

public void DoSomething(int index, bool wasThirdParam = true, params ushort[] array) 

The compiler will automatically pass an empty array if it is not specified, and you get the added flexibility to either pass an array as a single argument or put the elements directly as variable length arguments to your method.

回答3:

I know it's an old question, and whilst this answer doesn't directly solve how to get around the limitations imposed by the compiler, method overloading is an alternative:

   public void DoSomething(int index, bool thirdParam = true){         DoSomething(index, new ushort[] {}, thirdParam);    }     public void DoSomething(int index, ushort[] array, bool thirdParam = true){        ...    } 

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