I think that there is a problem with the `find` and `pop` members of `tokenmap`: in `find_free_slot`, which is used by the `insert` member, you apply collision resolution to find an unused element of `store_` where the new element can be inserted, but the `find` and `pop` members do not employ a loop when looking up the given key (to account for the possibility that they key resulted in a collision when it was inserted). It could be, for example, that the element of the given key was placed at `ix + 3` by `find_free_slot`, in which case `find` and `pop` would fail to find the element. Also, there are some improvements that can be made: supporting an allocator type and getting rid of the floating-point arithmetic around where you check whether a doubling of the capacity can succeed (lines 175-176; you can use the `max_size` member of `std::vector` and halve the result, rather than double `store_.capacity()`). By the way, you might be interested in taking a look at the JDK implementation of Java's `java.util.HashMap` class because the bucketing strategy, and the use of an underlying array for storage, is very similar.