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Comment by pmarreck | Hacker News Reader

Well, to be charitable, fortunately you can use a style like you propose where values only flow as I've indicated... but you'd still have to contend with OPC (Other People's Code) and if the language allows it, you just know it will turn up somewhere and ruin your day! ;)

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Indeed. Although 'out' is rare, it occasionally does ruin my day. So I have created a set of extension methods [1][2] to remove them from my life (because it does physically enrage me whenever I see the need to use it).

[1] https://github.com/louthy/language-ext/blob/master/LanguageE...

[2] https://github.com/louthy/language-ext/blob/daa5a10028e9637b...

> but you'd still have to contend with OPC (Other People's Code) and if the language allows it, you just know it will turn up somewhere and ruin your day! ;)

Yes, like the standard library's Dictionary.TryGetValue()...

you can do

if (dict.ContainsKey(key)) return dict[key] else return null;

the only place where you can't avoid them are TryParse. And there it sort of makes sense - the value is sort of side effect

> if (dict.ContainsKey(key)) return dict[key] else return null;

Which isn't thread-safe. So it's not always a better option.

But Dictionary<TKey,TValue> isn't thread-safe anyway, unless not modified.

Calling TryGetValue will either return a value or not. Calling ContainsKey, followed by an index read can lead to a race condition that means the value isn't there any more.

This is correct (and unfortunate).

If I'm reading the source correctly you could still get the bucket index and before you return true and the value, have that value removed from the dictionary. There is no synchronization going on, so concurrent modifications are just as much a problem with TryGetValue as with other approaches. TryGetValue is not atomic either.

Ok, fair enough. My mistake. Glad I don't use the BCL collection types any more and stick to immutable maps, lists, and sets :)

I feel like out was important for marshalling into C++ code?

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