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by avlasyuk 3573 days ago
Local const reference prolongs the object lifetime[1]. There shouldn't be any problems whenever you use it in a for loop.

[1]: https://herbsutter.com/2008/01/01/gotw-88-a-candidate-for-th...
2 comments
dbaupp 3573 days ago
There definitely can be problems: the reference may escape the for loop, and the reference may be invalidated by a modification of the container (even for something "stable" like ordered_map, the referent may be removed).
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E6300 3573 days ago
If a pointer/reference escapes the loop you'll have problems whether the thing to the right of the colon is a reference or a copy. If it's a copy, the escaped reference will definitely be invalid once that iteration complete. If it's a reference, it will remain valid in more situations.
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dbaupp 3573 days ago
Yes, I believe that's what I was saying, but your comment sounds like it is disagreeing. Could you clarify?
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E6300 3573 days ago
Oh, okay, then. I thought you were saying that that was a problem specific to iterating by reference.
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gpderetta 3573 days ago
references prolong the lifetime of temporaries. It wouldn't work in this case:

vector<int> v =...; const auto& x = v[59]; v.clear(); // x is dangling

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