'Design By Contract' in C#

Question

I wanted to try a little design by contract in my latest C# application and wanted to have syntax akin to:

public string Foo()
{
    set {
        Assert.IsNotNull(value);
        Assert.IsTrue(value.Contains("bar"));
        _foo = value;
    }
}

I know I can get static methods like this from a unit test framework, but I wanted to know if something like this was already built-in to the language or if there was already some kind of framework floating around. I can write my own Assert functions, just don't want to reinvent the wheel.

Answer 1

Aside from using an external library, you have a simple assert in System.Diagnostics:

using System.Diagnostics

Debug.Assert(value != null);
Debug.Assert(value == true);

Not very useful, I know.

Answer 2

You can use a Design By Contract implementation from sharp-architecture. Here is the link: http://code.google.com/p/sharp-architecture/

Regards,

Liang

Answer 3

You may want to check out nVentive Umbrella:

using System;
using nVentive.Umbrella.Validation;
using nVentive.Umbrella.Extensions;

namespace Namespace
{
    public static class StringValidationExtensionPoint
    {
        public static string Contains(this ValidationExtensionPoint<string> vep, string value)
        {
            if (vep.ExtendedValue.IndexOf(value, StringComparison.InvariantCultureIgnoreCase) == -1)
                throw new ArgumentException(String.Format("Must contain '{0}'.", value));

            return vep.ExtendedValue;
        }
    }

    class Class
    {
        private string _foo;
        public string Foo
        {
            set
            {
                _foo = value.Validation()
                    .NotNull("Foo")
                    .Validation()
                    .Contains("bar");
            }
        }
    }
}

I wish the Validation extensions were builders so you could do _foo = value.Validation().NotNull("Foo").Contains("bar").Value; but it is what it is (fortunately its open source so making it a builder is a trivial change).

And as an alternative solution you could consider domain validation.

Finally the new M languages, as part of Oslo, support restrictions on their extents and fields which translate both to T-SQL validation and a CLR class with functioning validation tests (though Oslo is a long time off from release).

Answer 4

Try LinFu's DesignByContract Library:

http://www.codeproject.com/KB/cs/LinFu_Part5.aspx

Answer 5

Looking over the code for Moq I saw that they use a class called 'Guard' that provides static methods for checking pre and post conditions. I thought that was neat and very clear. It expresses what I'd be thinking about when implementing design by contract checks in my code.

e.g.

public void Foo(Bar param)
{
   Guard.ArgumentNotNull(param);
} 

I thought it was a neat way to express design by contract checks.

Answer 6

For my current project (february 2010, VS 2008) I've choose http://lightcontracts.codeplex.com/

Simple, it's just runtime validation, without any weird complexity, you don't need to derive from some 'strange' base classes, no AOP, VS integration which won't work on some developer workstations, etc.

Simplicity over complexity.