params Parameter with default parameter values [duplicate]

问题

I've seen the params parameter more times than I can say and always removed it without thinking about it's meaning. Now I've learned its purpose. What I just learned is that the params parameter must be the last in the parameter list. But this is what I learned about the parameters that have a default value specified. Example:

MyMethod(string Name, int blah=0).

So the question is if I need to specify a default value as above while needing to use params, can this be done? If so, which must be declared last? Example:

MyMethod(int blah=0, params string[] variableData).

Thanks for your help again. James

回答1:

Your example is correct:

public void TestMethod(string name = "asdasd", params int[] items)
{
}

params has to be last, no matter what parameter are used before that.

回答2:

Yes, params are a special case here - they're the only situation in which a parameter without a default value can come after one with a default value.

However, you can't then call the method and take advantage of the params side of things (for a non-empty array) without also specifying the optional parameter:

MyMethod(5, "x", "y");                            // Fine, no defaulting
MyMethod(variableData: new string[] { "x", "y"}); // Default for blah
MyMethod();                                       // Default for blah, empty variableData
MyMethod(new string[] { "x, "y" });               // Invalid   
MyMethod("x", "y");                               // Invalid

来源：https://stackoverflow.com/questions/15129296/params-parameter-with-default-parameter-values

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params