llvm::iterator_facade_base

Description

Use this when it is reasonable to implement most of the iterator functionality in terms of a core subset. If you need special behavior or there are performance implications for this, you may want to override the relevant members instead.

Note, one abstraction that this does not provide is implementing subtraction in terms of addition by negating the difference. Negation isn't always information preserving, and I can see very reasonable iterator designs where this doesn't work well. It doesn't really force much added boilerplate anyways.

Another abstraction that this doesn't provide is implementing increment in terms of addition of one. These aren't equivalent for all iterator categories, and respecting that adds a lot of complexity for little gain.

Iterators are expected to have const rules analogous to pointers, with a single, const-qualified operator*() that returns ReferenceT. This matches the second and third pointers in the following example:

int Value;
{ int *I = &Value; }             // ReferenceT 'int&'
{ int *const I = &Value; }       // ReferenceT 'int&'; const
{ const int *I = &Value; }       // ReferenceT 'const int&'
{ const int *const I = &Value; } // ReferenceT 'const int&'; const

If an iterator facade returns a handle to its own state, then T (and PointerT and ReferenceT) should usually be const-qualified. Otherwise, if clients are expected to modify the handle itself, the field can be declared mutable or use const_cast.

Classes wishing to use iterator_facade_base should implement the following methods:

Forward Iterators: (All of the following methods)

• DerivedT &operator=(const DerivedT &R);

• bool operator==(const DerivedT &R) const;

• T &operator*() const;

• DerivedT &operator++();

Bidirectional Iterators: (All methods of forward iterators, plus the following)

• DerivedT &operator--();

Random-access Iterators: (All methods of bidirectional iterators excluding the following)

• DerivedT &operator++();

• DerivedT &operator--(); (and plus the following)

• bool operator<(const DerivedT &RHS) const;

• DifferenceTypeT operator-(const DerivedT &R) const;

• DerivedT &operator+=(DifferenceTypeT N);

• DerivedT &operator-=(DifferenceTypeT N);