How to examine value inside c# predicate parameter? - Determining predicate equality

I'm trying to determine the equality of two predicates:

public T FirstOrDefault(Func<T, bool> predicate)
{
    if (EntityCache.ContainsKey(predicate.GetHashCode()))
        return EntityCache[predicate.GetHashCode()];
    else
    {
        var entity = _objectSet.FirstOrDefault<T>(predicate);
        EntityCache.Add(predicate.GetHashCode(), entity);
        return entity;
    }
}

The issue I'm having is the hash code of the predicate开发者_JAVA百科 doesn't account for the values used inside it, and I'm not sure how to go about retrieving them.

If for instance the predicate passed to our method above is: (r => r.Id == id) how would I go about finding the value of 'id' inside my FirstOrDefault method?

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You'll need to use Expression's. They contains func's, but they also contain the syntax tree and you can examine their 'source code' at runtime.

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If I understand you correctly, you're trying to determine the value of a captured variable inside a delegate. I'm pretty sure there's no easy way to do this... perhaps if you used an expression tree instead of a delegate it would be simpler ? Another option (probably much simpler) is keeping the values passed to the delegates alongside them in EntityCache

Also note that instead of

if (EntityCache.ContainsKey(predicate.GetHashCode()))
    return EntityCache[predicate.GetHashCode()];

It would be better to use TryGetValue