Code contracts on auto-implemented properties

Question

Is there any way to put contracts on automatically implemented properties in .NET? (And how if the answer is 'Yes')?

(I assume using .NET code contracts from DevLabs)

Answer 1

Yes, this is possible - all that is needed is to add your contract condition to the [ContractInvariantMethod] method in your class, which then adds the equivalent Requires precondition to the automatic setter, and a post condition Ensures is added to the get. From section 2.3.1 of the Reference

As the example illustrates, invariants on auto-properties turn into:

1. A precondition for the setter
2. A postcondition for the getter
3. An invariant for the underlying backing field

And by example:

public int MyProperty { get; private set ;}

[ContractInvariantMethod]
private void ObjectInvariant ()
{
  Contract.Invariant ( this.MyProperty >= 0 );
}

"Is equivalent to the following code:"

private int backingFieldForMyProperty;
public int MyProperty 
{
  get 
  {
    Contract.Ensures(Contract.Result<int>() >= 0);
    return this.backingFieldForMyProperty;
  }

  private set 
  {
    Contract.Requires(value >= 0);
    this.backingFieldForMyProperty = value;
  }
}

[ContractInvariantMethod]
private void ObjectInvariant () 
{
  Contract.Invariant ( this.backingFieldForMyProperty >= 0 );
...

Answer 2

I'm thinking not, but you could easily write a snippet that would do this. If you go this route, here is a free snippet editor that will make the task very easy.