What does question mark and dot operator mean in C 6 0

Question

With C  6 0 in the VS2015 preview we have a new operator      which can be used like this   public class A      string PropertyOfA   get  set            var a   new A    var foo    bar   if a  PropertyOfA    foo         somecode     What exactly does it do

User · Answer

It can be very useful when flattening a hierarchy and/or mapping objects. Instead of:

if (Model.Model2 == null
  || Model.Model2.Model3 == null
  || Model.Model2.Model3.Model4 == null
  || Model.Model2.Model3.Model4.Name == null)
{
  mapped.Name = "N/A"
}
else
{
  mapped.Name = Model.Model2.Model3.Model4.Name;
}

It can be written like (same logic as above)

mapped.Name = Model.Model2?.Model3?.Model4?.Name ?? "N/A";

DotNetFiddle.Net Working Example.

(the ?? or null-coalescing operator is different than the ? or null conditional operator).

It can also be used out side of assignment operators with Action. Instead of

Action<TValue> myAction = null;

if (myAction != null)
{
  myAction(TValue);
}

It can be simplified to:

myAction?.Invoke(TValue);

DotNetFiddle Example:

using System;

public class Program
{
  public static void Main()
  {
    Action<string> consoleWrite = null;

    consoleWrite?.Invoke("Test 1");

    consoleWrite = (s) => Console.WriteLine(s);

    consoleWrite?.Invoke("Test 2");
  }
}

Result:

Test 2

User · Answer

It s the null conditional operator  It basically means    Evaluate the first operand  if that s null  stop  with a result of null  Otherwise  evaluate the second operand  as a member access of the first operand     In your example  the point is that if a is null  then a  PropertyOfA will evaluate to null rather than throwing an exception - it will then compare that null reference with foo  using string s    overload   find they re not equal and execution will go into the body of the if statement   In other words  it s like this   string bar    a    null   null   a PropertyOfA   if  bar    foo                    except that a is only evaluated once   Note that this can change the type of the expression  too  For example  consider FileInfo Length  That s a property of type long  but if you use it with the null conditional operator  you end up with an expression of type long    FileInfo fi           fi could be null long  length   fi  Length     If fi is null  length will be null

User · Answer

This is relatively new to C  which makes it easy for us to call the functions with respect to the null or non-null values in method chaining  old way to achieve the same thing was  var functionCaller   this member  if  functionCaller   null      functionCaller someFunction var someParam    and now it has been made much easier with just  member  someFunction var someParam    I strongly recommend this doc page

[c#] What does question mark and dot operator ?. mean in C# 6.0?

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