AutoHasher

Automatic generation of GetHashCode() methods using on the fly run-time code generation.

1. Advantages

Using this framework is a real treat. Here is what you get:

Productivity! You are guaranteed to generate a sound hash code. No more forgetting to update your hash code methods when adding or removing fields from your classes!
This framework run-time generates code that is as fast as hand coded implementations. Sometimes even faster since we utilize some optimization tricks.
You are automatically ensured to follow best practices- such as calculating inside an 'unchecked' block.
Automatic null handling.
Use the same implementation everywhere. Set up your editor to automatically insert the GetHashCode() when creating new classes.

2. Usage

1. Define a class

using AutoHash;
using AutoHash.Attributes;
class Foo
{
  internal string field1 = "foo";
  internal int bar = 42;
  internal List<int> l1 = null;
  internal List<int> l2 = new List<int>() { 0, 0 };

  [DontHash]
  internal string nonHashed = "boo";
}

2. Implement GetHashCode() the same way for all classes

public override int GetHashCode()
{
  return AutoHasher.GetHashCode(this);
}

3. Check that it works

[TestFixture]
class UsageTest
{
  [Test]
  public void TestUsage()
  {
    var foo = new Foo();
    int expected = 0;
    expected = (expected * 397) ^ foo.field1.GetHashCode();
    expected = (expected * 397) ^ foo.bar.GetHashCode();
    expected = (expected * 397) ^ foo.l2.Count.GetHashCode();

    int actual = foo.GetHashCode();

    Assert.AreEqual(expected, actual);
  }
}

Notice that the field 'nonHashed' is not part of the hash code, and the collections are only participating with their length.

kbilsted / AutoHasher