|Category: iterators||Component type: concept|
|Value type||The type of the value obtained by dereferencing a Trivial Iterator|
|X||A type that is a model of Trivial Iterator|
|T||The value type of X|
|x, y||Object of type X|
|t||Object of type T|
A Trivial Iterator may have a singular value, meaning that the results of most operations, including comparison for equality, are undefined. The only operation that a is guaranteed to be supported is assigning a nonsingular iterator to a singular iterator.
A Trivial Iterator may have a dereferenceable value, meaning that dereferencing it yields a well-defined value. Dereferenceable iterators are always nonsingular, but the converse is not true. For example, a null pointer is nonsingular (there are well defined operations involving null pointers) even thought it is not dereferenceable.
Invalidating a dereferenceable iterator means performing an operation after which the iterator might be nondereferenceable or singular. For example, if p is a pointer, then delete p invalidates p.
|Name||Expression||Type requirements||Return type|
|Default constructor||X x|
|Dereference||*x||Convertible to T |
|Dereference assignment||*x = t||X is mutable|
|Member access||x->m ||T is a type for which x.m is defined|
|Default constructor||X x||x is singular|
|Dereference||*x||x is dereferenceable|
|Dereference assignment||*x = t||x is dereferenceable||*x is a copy of t|
|Member access||x->m||x is dereferenceable||Equivalent to (*x).m|
|Identity||x == y if and only if &*x == &*y|
 The requirement for the return type of *x is specified as "convertible to T", rather than simply T, because it sometimes makes sense for an iterator to return some sort of proxy object instead of the object that the iterator conceptually points to. Proxy objects are implementation details rather than part of an interface (one use of them, for example, is to allow an iterator to behave differently depending on whether its value is being read or written), so the value type of an iterator that returns a proxy is still T.
 Defining operator-> for iterators depends on a feature that is part of the C++ language but that is not yet widely implemented by C++ compilers. It is therefore not implemented in this release; once compilers that support it become more common, future releases of the STL will provide operator-> for iterators. In the mean time, the workaround is to use (*it).m instead of it->m.