[iterator.cpp17] - C++20 → C++23

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tmp/tmpjutysguy/{from.md → to.md} +21 -16

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@@ -1,7 +1,9 @@
 ### C++17 iterator requirements <a id="iterator.cpp17">[[iterator.cpp17]]</a>
 In the following sections, `a` and `b` denote values of type `X` or
 `const X`, `difference_type` and `reference` refer to the types
 `iterator_traits<X>::difference_type` and
 `iterator_traits<X>::reference`, respectively, `n` denotes a value of
 `difference_type`, `u`, `tmp`, and `m` denote identifiers, `r` denotes a
@@ -16,19 +18,18 @@ value of some type that is writable to the output iterator.
 The *Cpp17Iterator* requirements form the basis of the iterator
 taxonomy; every iterator meets the *Cpp17Iterator* requirements. This
 set of requirements specifies operations for dereferencing and
 incrementing an iterator. Most algorithms will require additional
 operations to read [[input.iterators]] or write [[output.iterators]]
-values, or to provide a richer set of iterator movements (
-[[forward.iterators]], [[bidirectional.iterators]],
-[[random.access.iterators]]).
-A type `X` meets the *Cpp17Iterator* requirements if:
-- `X` meets the *Cpp17CopyConstructible*, *Cpp17CopyAssignable*, and
-  *Cpp17Destructible* requirements [[utility.arg.requirements]] and
- lvalues of type `X` are swappable [[swappable.requirements]], and
 - `iterator_traits<X>::difference_type` is a signed integer type or
   `void`, and
 - the expressions in [[iterator]] are valid and have the indicated
   semantics.
@@ -50,31 +51,35 @@ uses that algorithm makes of `==` and `!=`.
 [*Example 1*: The call `find(a,b,x)` is defined only if the value of
 `a` has the property *p* defined as follows: `b` has property *p* and a
 value `i` has property *p* if (`*i==x`) or if (`*i!=x` and `++i` has
 property *p*). — *end example*]
 [*Note 1*: For input iterators, `a == b` does not imply `++a == ++b`.
 (Equality does not guarantee the substitution property or referential
-transparency.) Algorithms on input iterators should never attempt to
-pass through the same iterator twice. They should be *single pass*
-algorithms. Value type `T` is not required to be a *Cpp17CopyAssignable*
-type ([[cpp17.copyassignable]]). These algorithms can be used with
-istreams as the source of the input data through the `istream_iterator`
-class template. — *end note*]
 #### Output iterators <a id="output.iterators">[[output.iterators]]</a>
 A class or pointer type `X` meets the requirements of an output iterator
 if `X` meets the *Cpp17Iterator* requirements [[iterator.iterators]] and
 the expressions in [[outputiterator]] are valid and have the indicated
 semantics.
 [*Note 1*: The only valid use of an `operator*` is on the left side of
 the assignment statement. Assignment through the same value of the
-iterator happens only once. Algorithms on output iterators should never
-attempt to pass through the same iterator twice. They should be
-single-pass algorithms. Equality and inequality might not be
 defined. — *end note*]
 #### Forward iterators <a id="forward.iterators">[[forward.iterators]]</a>
 A class or pointer type `X` meets the requirements of a forward iterator

 ### C++17 iterator requirements <a id="iterator.cpp17">[[iterator.cpp17]]</a>
+#### General <a id="iterator.cpp17.general">[[iterator.cpp17.general]]</a>
 In the following sections, `a` and `b` denote values of type `X` or
 `const X`, `difference_type` and `reference` refer to the types
 `iterator_traits<X>::difference_type` and
 `iterator_traits<X>::reference`, respectively, `n` denotes a value of
 `difference_type`, `u`, `tmp`, and `m` denote identifiers, `r` denotes a
 The *Cpp17Iterator* requirements form the basis of the iterator
 taxonomy; every iterator meets the *Cpp17Iterator* requirements. This
 set of requirements specifies operations for dereferencing and
 incrementing an iterator. Most algorithms will require additional
 operations to read [[input.iterators]] or write [[output.iterators]]
+values, or to provide a richer set of iterator movements
+[[forward.iterators]], [[bidirectional.iterators]], [[random.access.iterators]].
+A type `X` meets the requirements if:
+- `X` meets the *Cpp17CopyConstructible*, *Cpp17CopyAssignable*,
+  *Cpp17Swappable*, and *Cpp17Destructible* requirements
+ [[utility.arg.requirements]], [[swappable.requirements]], and
 - `iterator_traits<X>::difference_type` is a signed integer type or
   `void`, and
 - the expressions in [[iterator]] are valid and have the indicated
   semantics.
 [*Example 1*: The call `find(a,b,x)` is defined only if the value of
 `a` has the property *p* defined as follows: `b` has property *p* and a
 value `i` has property *p* if (`*i==x`) or if (`*i!=x` and `++i` has
 property *p*). — *end example*]
+*Recommended practice:* The implementation of an algorithm on input
+iterators should never attempt to pass through the same iterator twice;
+such an algorithm should be a single pass algorithm.
 [*Note 1*: For input iterators, `a == b` does not imply `++a == ++b`.
 (Equality does not guarantee the substitution property or referential
+transparency.) Value type `T` is not required to be a
+*Cpp17CopyAssignable* type ([[cpp17.copyassignable]]). Such an
+algorithm can be used with istreams as the source of the input data
+through the `istream_iterator` class template. — *end note*]
 #### Output iterators <a id="output.iterators">[[output.iterators]]</a>
 A class or pointer type `X` meets the requirements of an output iterator
 if `X` meets the *Cpp17Iterator* requirements [[iterator.iterators]] and
 the expressions in [[outputiterator]] are valid and have the indicated
 semantics.
+*Recommended practice:* The implementation of an algorithm on output
+iterators should never attempt to pass through the same iterator twice;
+such an algorithm should be a single-pass algorithm.
 [*Note 1*: The only valid use of an `operator*` is on the left side of
 the assignment statement. Assignment through the same value of the
+iterator happens only once. Equality and inequality are not necessarily
 defined. — *end note*]
 #### Forward iterators <a id="forward.iterators">[[forward.iterators]]</a>
 A class or pointer type `X` meets the requirements of a forward iterator

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