Question

Possible Duplicate:
passing an empty array as default value of optional parameter in c#

I have a method that looks like below. Currently, the parameter tags is NOT optional

void MyMethod(string[] tags=null)
{
   tags= tags ?? new string[0];
   /*More codes*/
}

I want to make parameter tags optional, as per c# , to make a parameter optional you can set a default value in method signature. I tried the following hacks but none worked.

Code that didn’t work – 1

void MyMethod(string[] tags=new string[0]){}

Code that didn’t work – 2

void MyMethod(string[] tags={}){}

Please suggest what I am missing.

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I have already seen this question:

Passing an empty array as default value of an optional parameter

Answer 1

The documentation for optional arguments says:

A default value must be one of the following types of expressions:

• a constant expression;

• an expression of the form new ValType(), where ValType is a value type, such as an enum or a struct;

• an expression of the form default(ValType), where ValType is a value type.

Since new string[0] is neither a constant expression nor a new statement followed by a value type, it cannot be used as a default argument value.

The first code excerpt in your question is indeed a good workaround:

void MyMethod(string[] tags = null)
{
   tags = tags ?? new string[0];
   // Now do something with 'tags'...
}