Null parameter alternative C# 6.0

Question

I have seen new feature in C# 6 which allows code to skip if statements for null checks.

For example:

return p?.ToString();

How can this be done for calling a method to which p needs to be passed as parameter (without old if/else)?

The way I would normally write this with C# pre-6:

 p != null ? callmethod(p) : null

is there something better in C# 6?

Answer 1

You can use an extension method - which you can generalize to any situation. This works because C# allows extension methods to work with null values for the this parameter (surprisingly!), whereas with normal instance methods you would otherwise get a NullReferenceException.

Here's something similar to what I used in my own projects before we had the ?. "safe-navigation" operator in C# 6:

public static class Extensions
{    
    public static TRet NullSafeCall<TValue,TRet>( this TValue value, Func<TValue,TRet> func )
        where TValue : class
        where TRet : class
    {
        if( value != null ) return func( value );
        return null;
    }
}

Used like so:

return p.NullSafeCall( callmethod );

It also supports the use of lambdas if you need to pass more than 1 argument into your subsequent func:

String foo = "bar";
return p.NullSafeCall( v => callmethod2( v, foo ) );

In your example you used String.IsNullOrEmpty instead of != null, which can be added like so:

public static class Extensions
{    
    public static TRet NullSafeCall<TValue,TRet>( this TValue value, Func<TValue,Boolean> guard, Func<TValue,TRet> func )
        where TValue : class
        where TRet : class
    {
        if( guard( value ) ) return func( value );
        return null;
    }
}

Usage:

return p.NullSafeCall( v => String.IsNullOrEmpty( v ), v => callmethod( v ) );

And of course, you can chain it:

return p
    .NullSafeCall( callmethod2 )
    .NullSafeCall( callmethod3 )
    .NullSafeCall( v => callmethod4( v, "foo", bar ) );