4 This allows iteration over arrays, lists, maps, trees, etc. in a unified way. |
4 This allows iteration over arrays, lists, maps, trees, etc. in a unified way. |
5 |
5 |
6 Creating an iterator is as simple as creating a `CxIterator` struct and setting the fields in a meaningful way. |
6 Creating an iterator is as simple as creating a `CxIterator` struct and setting the fields in a meaningful way. |
7 The UCX collections provide various functions to create such iterators. |
7 The UCX collections provide various functions to create such iterators. |
8 |
8 |
9 If the predefined fields are insufficient (or introduce too much bloat) for your use case, |
9 If the predefined fields are not enough (or introduce too much bloat) for your use case, |
10 you can alternatively create your own iterator structure |
10 you can alternatively create your own iterator structure |
11 and place the `CX_ITERATOR_BASE` macro as first member of that structure. |
11 and place the `CX_ITERATOR_BASE` macro as first member of that structure. |
12 |
12 |
13 ```C |
13 ```C |
14 #include <cx/iterator.h> |
14 #include <cx/iterator.h> |
77 The macro takes three arguments: |
77 The macro takes three arguments: |
78 1. the pointer-type of a pointer to an element, |
78 1. the pointer-type of a pointer to an element, |
79 2. the name of the variable you want to use for accessing the element, |
79 2. the name of the variable you want to use for accessing the element, |
80 3. and the iterator. |
80 3. and the iterator. |
81 |
81 |
82 > An iterator does not necessarily need to iterate over the elements of a collections. |
82 > An iterator does not necessarily need to iterate over the concrete elements of a collection. |
83 > Map iterators, for example, can iterator over the key/value pairs, |
83 > Map iterators, for example, can iterator over the key/value pairs, |
84 > but they can also iterate over just the values or just the keys. |
84 > but they can also iterate over just the values or just the keys. |
85 > |
85 > |
86 > You should read the documentation of the function creating the iterator to learn |
86 > You should read the documentation of the function creating the iterator to learn |
87 > what exactly the iterator is iterating over. |
87 > what exactly the iterator is iterating over. |
98 If you are implementing your own iterator, it is up to you to implement this behavior. |
98 If you are implementing your own iterator, it is up to you to implement this behavior. |
99 |
99 |
100 ## Passing Iterators to Functions |
100 ## Passing Iterators to Functions |
101 |
101 |
102 To eliminate the need of memory management for iterators, the structures are usually used by value. |
102 To eliminate the need of memory management for iterators, the structures are usually used by value. |
103 This does not come with additional costs, because iteration is implemented entirely by macros. |
103 This does not come with additional costs because iteration is implemented entirely by using macros. |
104 |
104 |
105 However, sometimes it is necessary to pass an iterator to another function. |
105 However, sometimes it is necessary to pass an iterator to another function. |
106 To make that possible in a generalized way, such functions should accept a `CxIteratorBase*` pointer |
106 To make that possible in a generalized way, such functions should accept a `CxIteratorBase*` pointer |
107 which can be obtained with the `cxIteratorRef()` macro on the calling site. |
107 which can be obtained with the `cxIteratorRef()` macro on the calling site. |
108 |
108 |
143 |
143 |
144 Iterators may be wrapped in which case the original implementation can be stored in `current_impl` and |
144 Iterators may be wrapped in which case the original implementation can be stored in `current_impl` and |
145 called by a wrapper implementation pointed to by `current`. |
145 called by a wrapper implementation pointed to by `current`. |
146 This can be useful when you want to support the `store_pointer` field of the [](collection.h.md) API. |
146 This can be useful when you want to support the `store_pointer` field of the [](collection.h.md) API. |
147 |
147 |
148 A specialized, simple, and fast iterator over an array of a certain type, |
148 A specialized, simple, and fast iterator over an array of a certain type |
149 that does not support mutation, can be implemented as follows: |
149 that does not support mutation can be implemented as follows: |
150 ```C |
150 ```C |
151 #include <cx/iterator.h> |
151 #include <cx/iterator.h> |
152 |
152 |
153 typedef struct my_foo_s { |
153 typedef struct my_foo_s { |
154 // ... your data ... |
154 // ... your data ... |
194 } |
194 } |
195 ``` |
195 ``` |
196 |
196 |
197 > Note, that the behavior of `current` is undefined when `valid` returns `false`. |
197 > Note, that the behavior of `current` is undefined when `valid` returns `false`. |
198 > That means, on the one hand, `current` does not need to check for validity of the iterator, |
198 > That means, on the one hand, `current` does not need to check for validity of the iterator, |
199 > but on the other hand it is forbidden to invoke `current` when `valid` would return `false`. |
199 > but on the other hand, it is forbidden to invoke `current` when `valid` would return `false`. |
200 {style="note"} |
200 {style="note"} |
201 |
201 |
202 > If performance matters in your application, it is recommended that you indeed create specialized iterators |
202 > If performance matters in your application, it is recommended that you indeed create specialized iterators |
203 > for your collections. The default UCX implementations trade some of the performance for generality. |
203 > for your collections. The default UCX implementations trade some performance for generality. |
204 |
204 |
205 <seealso> |
205 <seealso> |
206 <category ref="apidoc"> |
206 <category ref="apidoc"> |
207 <a href="https://ucx.sourceforge.io/api/iterator_8h.html">iterator.h</a> |
207 <a href="https://ucx.sourceforge.io/api/iterator_8h.html">iterator.h</a> |
208 </category> |
208 </category> |