TotalContainer.length
size_t length() @propertyReturns the number of elements in the container.
Complexity: log(n).
void length(size_t newLength) @propertySets the number of elements in the container to newSize. If newSize is greater than length, the added elements are added to unspecified positions in the container and initialized with .init.
Complexity: abs(n - newLength)
Postcondition: _length == newLength