Compute hash of class code at runtime (C#)?

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+2 Q:

Compute hash of class code at runtime (C#)?

Is it possible to compute the hash of a class at runtime in C# (presumably through reflection)? To be clear, I don't want to compute the hashcode of an instance of said class, I want to compute the hash of the class code itself (if a function in the class changes, I'd expect a different hash code to be computed). Ideally this would only be sensitive to changes in the object code (and not just a hash of the string representation of the code itself).

Thanks in advance for your help,

-- Breck

+1 A:

You don't need to use reflection. You can try System.Type.GetHashCode(). I'm not sure how it works, if not optimal, than you can always use type.FullName.GetHashCode()

Andrew Bezzub 2010-03-19 20:46:07

Type.GetHashCode() seems to change its value between recompiles. type.FullName.GetHashCode() wouldnt' change hashes for when a method changes.

Jimmy 2010-03-19 20:48:47

System.Type.GetHashCode will work just fine, it will change if a method name changes or a parameter name / type changes, etc., type.FullName.GetHashCode will not work as the type name could stay the same but a method might change.

John JJ Curtis 2010-03-19 20:48:58

@Jeff: class Program { static void Main() { Console.Write(typeof(Program).GetHashCode(); } } changes its output between compiles.

Jimmy 2010-03-19 20:50:53

@Jimmy You're right, I should have run my test twice with the same exact class, sorry...

John JJ Curtis 2010-03-19 22:10:50

+3 A:

If you have the Type you can use GetMethod to get an instance of MethodInfo, which in turn has a GetMethodBody that returns the IL for said method. You can then hash that.

I am curious. Why do you want to do this in the first place?

Brian Rasmussen 2010-03-19 20:49:54

The reason I want to do this is that in my case I have a function, f, of considerable time complexity. The problem is that I'm experimenting with the values f should be returning, so f changes frequently. If a particular version of f, fi, has already run for an input, x, I want to cache the result, fi(x) so that if fi runs again, it can just use the memoized value.

Breck Fresen 2010-03-19 21:42:40

Thanks for the explanation.

Brian Rasmussen 2010-03-19 22:01:39

ansaurus

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Compute hash of class code at runtime (C#)?

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