NTuple

C++ does not have a built-in tuple-like container that can store a fixed-size tuple of values of the same type. This behavior can be achieved via manual typing std::tuple<T, T, T, ...> where T is the type of the values or via std::array<T, N> where N is the size of the tuple. I insist that std::array<T, N> is not semantically the same, so I wrote a custom abl::ntuple container that works the same way as abl::tuple.

Implementation details

The abl::ntuple container is implemented as a wrapper around a proxy struct that inherits from a pack of leaf structs, each of which holds a single value of the tuple. This makes the container occupy consecutive memory locations, allowing for efficient indexing and iteration via simple casts.

Constructors

abl::ntuple provides the following constructors:

• abl::ntuple(): default constructor, initializes a tuple with default-constructed values.
• abl::ntuple(Args&&...): initializes the tuple with the given values.
• abl::ntuple(abl::ntuple const&): copy constructor, copies the tuple.
• abl::ntuple(abl::ntuple&&): move constructor, transfers ownership of the tuple.

Assignment operators

abl::ntuple provides the following assignment operators:

• abl::ntuple& operator=(abl::ntuple const&): copy assignment operator, copies the tuple.
• abl::ntuple& operator=(abl::ntuple&&): move assignment operator, transfers ownership of the tuple.

Modifiers

abl::ntuple provides the following modifiers:

• void swap(abl::ntuple&): swaps the contents of the tuple with another tuple.

Accessors

abl::ntuple provides the following accessors:

• T& get<I>() &: returns a reference to the value at the given index I.
• T const& get<I>() const &: returns a const reference to the value at the given index I.
• T&& get<I>() &&: returns a rvalue reference to the value at the given index I.
• T const&& get<I>() const &&: returns a const rvalue reference to the value at the given index I.

Observers

abl::ntuple provides the following observers:

• static std::size_t size returns the number of elements in the tuple.

Comparison operators

abl::ntuple provides the following comparison operators:

• bool operator==(abl::ntuple const&): returns true if the tuples are equal, false otherwise.
• bool operator<=>(abl::ntuple const&): a three-way comparison operator that returns 0 if the tuples are equal, 1 if the first tuple is greater, and -1 if the second tuple is greater.

Non-member functions

abl::ntuple provides the following non-member functions:

• void swap(abl::ntuple&, abl::ntuple&): swaps the contents of two tuples.
• T& get<I>(abl::ntuple&): returns a reference to the value at the given index I.
• T const& get<I>(abl::ntuple const&): returns a const reference to the value at the given index I.
• T&& get<I>(abl::ntuple&&): returns a rvalue reference to the value at the given index I.
• T const&& get<I>(abl::ntuple const&&): returns a const rvalue reference to the value at the given index I.