Can somebody provide a example of this?
I have tried null,string.Empty and object initialization but they don't work since default value has to be constant at compile time
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7 Answers
Just use the null coalescing operator and an instance of empty List<string>
public void Process(string param1, List<string> param2 = null)
{
param2 = param2 ?? new List<string>();
// or starting with C# 8
param2 ??= new List<string>();
}
The problem with this is that if "param2" is null and you assign a new reference then it wouldn't be accessible in the calling context.
1 Comment
Pavan Keerthi
Yes,I get the limitation but this worked well for me in this case.
You may also do the following using default which IS a compile-time-constant (null in the case of a List<T>):
void DoSomething(List<string> lst = default(List<string>))
{
if (lst == default(List<string>)) lst = new List<string>();
}
You can simplify this even further to:
void DoSomething(List<string> lst = default)
answered Jul 30, 2015 at 7:34
MakePeaceGreatAgain
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1 Comment
PoorInRichfield
IntelliSense is showing me the statement can be simplified even further by just using "default" instead of "default(List<string>").
It is impossible. You should use method overloading instead.
public static void MyMethod(int x, List<string> y) { }
public static void MyMethod(int x)
{
MyMethod(x, Enumerable<string>.Empty());
}
As others mentioned you assign null to the optional parameter, in newer versions when using <Nullable>enable</Nullable> you need to mark the parameter with the nullable annotation (?) and assign a null value to it, otherwise it will cause error CS8625 - Cannot convert null literal to non-nullable reference type.
void DoSomething(string param, List<string>? optional = null)
{
// Check if the parameter is null, if so create empty list
optional ??= new();
...
}
Comments
private void test(List<string> optional = null)
{
}
sorry about the string instead of list. Null works fine for me on 4.0, i am using visual studio 2010
4 Comments
Domenic
That's
string, not List<string>Pavan Keerthi
It compiles ,but you get Object Instantiation exception at run time
Drake
I did not get that exception, make sure you test your answers before making the claim.
bsod_
Works fine for me, but needs to be at the end if you have multiple parameters
I like it this way, it is more readable then ??=
if (param == null) param = new();
Comments
private void test(params object[] params)
{
}
