问题
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){
...
}
来源：https://stackoverflow.com/questions/3480382/passing-an-empty-array-as-default-value-of-an-optional-parameter