CODEWITHSUNDEEP
c#
Aaron Thomas
Aaron Thomas

Reputation: 5281

C# nested class properties

In C#, why does a nested class have to instantiate it's parent class, to reference its parent class non-static properties in code?

public class OuterClass
{
    public int OuterClassProperty
    {
        get
        {
            return 1;
        }
    }

    public class InnerClass
    {
        public int InnerClassProperty
        {
            get
            {
                /* syntax error: cannot access a non-static
                 * member of outer type via nested type.
                 */
                return OuterClassProperty;
            }
        }
    }
}

It seems I have to do this instead:

public class OuterClass
{
    public int OuterClassProperty
    {
        get
        {
            return 1;
        }
    }

    public class InnerClass
    {
        public int InnerClassProperty
        {
            get
            {
                OuterClass ImplementedOuterClass = new OuterClass();
                return ImplementedOuterClass.OuterClassProperty;
            }
        }
    }
}

I'm thinking the first code example should be okay, because if InnerClass is instantiated, the parent class would implemented first - along with the parent class properties.

Thanks for the help, I'm trying to learn the in's and out's of C#... and I am not familiar with Java, comparing to Java won't help much...

Upvotes: 2

Views: 1729

Answers (1)

Alexei Levenkov
Alexei Levenkov

Reputation: 100547

The behavior you are observing is explicitly spelled out in the C# specification. Snippet of C# 5.0 below:

10.3.8.4 this access
A nested type and its containing type do not have a special relationship with regard to this-access (§7.6.7). Specifically, this within a nested type cannot be used to refer to instance members of the containing type. In cases where a nested type needs access to the instance members of its containing type, access can be provided by providing the this for the instance of the containing type as a constructor argument for the nested type.

The behavior of nested classes in C# is different for other language like Java inner classes in c# and C+ because C# is different language created by different language design team. Exact historical reasons why particular behavior was selected possibly could be found in blogs of members of C# design team, .Net design guidelines book or MSDN articles.

Upvotes: 5

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