ChallengeFind the slow down–answer
I asked about a slow piece of code and why it is so slow. The answer is pretty simple, I messed up, take a look at this piece of code:
When the Value is an int, I’m creating a span from the address of a long variable (initialized to zero). That means that I have a lot of hash collisions, which means that adding to the dictionary turned into a sequential operation, which means that the actual cost here is O(N**2).
Interestingly enough, you can’t write this code without the use of unsafe. I actually didn’t know that the scope of the variable was even valid here to have its address taken. That was very hard to debug, because the problem was hidden away somewhere very far from where we looked at.
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It makes sense that you can read the address of an uninitialized variable since you need to do it for scenarios like:
long l; SomeUnmanagedApi(&l, ...);
I was also wondering why 'l' was still in scope in the else, which I imagine so you can do things like
if (value is long l) DoSomething(l);
l = 0; DoSomethingElse(l);
It seems like a good static analysis tool should identify that the variable i is unused in the if(Value is int i) block, which means you've either got a bug or you should just write if(value is int).
what language is this?
This is in C#