For sure. I agree with you. If you know the number in advance back_inserter is not the most recommendable idiom. Furthermore, in general it is better a “oneliner” solution, if available, compared to a pair of statement (as in the case of reserve + copy) to do a conceptual operation.

I was going to express much the same sentiment, that the reallocation issue is defeated by reserve, but on reflection if you know how much to reserve you probably (though not necessarily) have all the elements in advance, so adding them one by one is not the most natural expression of intent. I grant you it’s a moot point. In fairness to Jonathan’s excellent blog site I had considered his use of back_inserter( ) as being for exposition, rather than a recommendation of the idiom.