C#: Declare that a function will never return null?

Background: There is this developer principle "Should my function return null or throw an exception if the requested item does not exist?" that I wouldn't like to discuss here. I decided to throw an exception for all cases that have to return a value and this value only wouldn't exist in cases of an (programmatically or logically) invalid reques开发者_开发知识库t.

And finally my question: Can I mark a function so that the compiler knows that it will never return null and warn anybody who checks if the return value is null?

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You can do this using Code Contracts.

Example :

    public String Method1()
    { 
        Contract.Ensures(Contract.Result<String>() != null);

        // To do
    }

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Using Code Contracts you can define a contract that a method does not return null.

using System.Diagnostics.Contracts; // required namespace 

public T MethodName()
{
    Contract.Ensures(Contract.Result<T>() != null); //where T is the return type.

    // method body...
}

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You are looking for Code Contracts

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If you return a value type, then it can't be null (unless you explicitly make it so using the system 'nullable' wrapper).