Make performance description of String::insert_str more precise #138538
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I don't really see why anyone would need such precise numbers, it's not like you could correlate that with an exact cycle number or something.
Still, the old note is not correct. I recommend you adapt the old note to say something about the tail of the string needing to be shifted – that is probably the most helpful information to anyone investigating a performance issue in their code.
| /// This is an *O*(*n*) operation as it requires copying every element in the | ||
| /// buffer. | ||
| /// If there is space in `self` this will copy `self.len() - idx + string.len()` bytes, | ||
| /// otherwise will reallocate and copy `self.len() + string.len()` bytes. |
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This is incorrect – the reallocation case potentially copies self.capacity() bytes and then additionally self.len() - idx + string.len() bytes.
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Being too specific also has the downside that it's essentially specifying the implementation, thus constraining future implementation changes. What is documented generally is a guarantee. |
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