From https://stackoverflow.com/q/66755218

[tab:cpp17.allocator] has the following example added by p0593r6:

When reusing storage denoted by some pointer value p, launder(reinterpret_­cast<T*>(new (p) byte[n * sizeof(T)])) can be used to implicitly create a suitable array object and obtain a pointer to it.

If T is not an implicit-lifetime type, then, even if an object of type T[m ≤ n] is created, the lifetimes of the array elements are not started, which means launder's preconditions are violated:

Preconditions: p represents the address A of a byte in memory. An object X that is within its lifetime and whose type is similar to T is located at the address A.