How to not duplicate Code Contracts checks?

Question

I have static class which contains methods with same signatures.

static class SomeClass
{
    static void SomeMethod(int param)
    {
        Contract.Requires<ArgumentException>(param != 0);
        // some code
    }

    static void SomeMethod2(int param)
    {
        Contract.Requires<ArgumentException>(param != 0);
        // some code
    }
}

Is there any way to not duplicate CodeContract checks in this methods?

Answer 1

You can use a contract abbreviator. But personally I would not do it for this kind of simple check. Here's an example for an abbreviator we use:

public static class ContractEx
{
    [ContractAbbreviator]
    public static void StringNullOrEmpty(string s, string parameterName)
    {
        Contract.Requires<ArgumentNullException>(s != null, parameterName);
        Contract.Requires<ArgumentException>(s.Length != 0, parameterName);
        Contract.Requires(!String.IsNullOrEmpty(s));  // required for static code analysis
    }
}

Usage:

void SomeMethod(string foo)
{
    ContractEx.StringNullOrEmpty(foo, "foo");
}

Note this has the distinct disadvantage of having to specify the parameter name yourself. You can omit it, but then the contracts rewriter would emit an exception with s != null as the condition that failed, which makes no sense for an argument exception.

Abbreviators usually make more sense as instance methods that check the state of a class. For example (from MSDN):

[ContractAbbreviator]
private void DataAndStateUnchanged() 
{
   Contract.Ensures(this.State == Contract.OldValue(this.State));
   Contract.Ensures(this.Data == Contract.OldValue(this.Data));
}