Similarly, I once ran into a broken implementation of a Dictionary type (in Mono, I think.) It was only comparing the keys' hash codes, not the keys themselves.

Similarly, I once ran into a broken implementation of a Dictionary type (in Mono, I think.) It was only comparing the keys' hash codes, not the keys themselves. In most scenarios this turned out to be more than good enough - for int32 keys obviously it will work, and for most strings it works too if the hash function is good - but I had a great many keys without an amazing hash function for them. It's funny how sometimes a really glaring bug can hide in a stdlib for months or years just because by luck the stars never align to trigger it where somebody can notice it. In my case, the dictionary bug was causing recoverable errors, and I only noticed because I dug in instead of going "Mono's just broken".