Nullable Func<T, TResult>

Question

In C# is it possible to pass a method a nullable Func?

Neither Func<A, bool>? nor Func?<A, bool> is working.

Zebulen

Answer 1

That doesn't make sense.
All reference types, including Func<...>, can already be null.

Nullable types apply to value types (structs), which cannot ordinarily be null.

Dominations

@bto.rdz: Huh? Javascript doesn't have type enforcement at all. – Dominations

Answer 2

A Func is a delegate which is a reference type. This means it is already nullable (you can pass null to a method).

Proctology

Answer 3

C# 1.0 - 7.x:

All reference types including Func as delegate, can be null by default.

C# > 8.x:

Func<T> must be marked as Func<T>? to be able to receive a null as default parameter value.

Example for C# 1.0 - 7.x:

/// <summary>
/// Returns an unique absolute path based on the input absolute path.
/// <para>It adds suffix to file name if the input folder already has the file with the same name.</para>
/// </summary>
/// <param name="absolutePath">An valid absolute path to some file.</param>
/// <param name="getIndex">A suffix function which is added to original file name. The default value: " (n)"</param>
/// <returns>An unique absolute path. The suffix is used when necessary.</returns>
public static string GenerateUniqueAbsolutePath(string absolutePath, Func<UInt64, string> getIndex = null)
{
    if (getIndex == null)
    {
        getIndex = i => $" ({i})";
    }
    // ... other logic
}

Example for >C# 8.x:

/// <summary>
/// Returns an unique absolute path based on the input absolute path.
/// <para>It adds suffix to file name if the input folder already has the file with the same name.</para>
/// </summary>
/// <param name="absolutePath">An valid absolute path to some file.</param>
/// <param name="getIndex">A suffix function which is added to original file name. The default value: " (n)"</param>
/// <returns>An unique absolute path. The suffix is used when necessary.</returns>
public static string GenerateUniqueAbsolutePath(string absolutePath, Func<UInt64, string>? getIndex = null)
{
    if (getIndex == null)
    {
        getIndex = i => $" ({i})";
    }
    // ... other logic
}

Placentation

Answer 4

Func -> Encapsulates a method that returns a type specified by generic parameter

If return type is void, There is a different delegate (Action)

Action ->Encapsulates a method that does not return a value.

If you require Func to accept parameters that can accept null (nullable type), or require Func to return value which may be null(nullable type), there is no restriction.

For Example.

    Func<int?, int?, bool> intcomparer = 
    (a,b)=>
    {
    if(a.HasValue &&b.HasValue &&a==b) 
        return true;
        return false;
    } ;

    Func<int?, int?, bool?> nullintcomparer = 
    (a,b)=>
    {

    if(a.HasValue &&b.HasValue &&a==b) 
        return true;
    if(!a.HasValue || !b.HasValue)
       return null;
        return false;
    } ;

    var result1 = intcomparer(null,null); //FALSE
    var result2 = intcomparer(1,null); // FALSE
    var result3 = intcomparer(2,2); //TRUE


    var result4 = nullintcomparer(null,null); // null
    var result5 = nullintcomparer(1,null); // null
    var result6 = nullintcomparer(2,2); //TRUE

Realtor

He isn't talking about the return type. – Dominations

this is answers the question I had when querying google. – Multiracial