UML Multiplicity

UML Multiplicity Categories

Mandatory & Optional Multivalued

• Multiplicity: [*] [0..2] [0..*] [1..*] [2..4]
• Containers:
• std::vector<int>
• std::deque<int>
• std::list<int>
• std::forward_list<int> (C++11)
• std::array<int, N> (C++11) where N is a constexpr

Optional Single Value

Optional Single Value: C++ Pointer

C++ Pointer Use

3 states of char*

std::string Record

2 States of std::string

Solution: Flag

• For each optional, have to maintain another flag variable
• Have to remember the relationship between name and hasName

Solution: std::optional

• C++17 feature, similar to boost::optional
• Can be used on any value type (non-pointer)
• Allows for lazy loading/allocation
• Complete replacement of having to use pointers for optional single-value attributes

Scalar Usage

Use Case: Represent Optional Types

Use Case: Error Return

Takeaway

• Use std::optional where you are mapping from an Optional type in UML
• Use std::optional in all cases where pointers are used to represent optional values