Adds initial draft for iterators topic

sources/knowledge_areas.dat

@@ -55,6 +55,8 @@ EH Error Handling
 	? ? ? ? errno
 	? ? ? ? Error Codes
 	eh y y y Exception Handling
+PD Program Design
+	it y y n Iterators
 SL Standard Library
 	? ? ? ? Input/Output (I/O)
 	? ? ? ? Containers, Iterators, and Algorithms

sources/modules/object-model/reference-semantics.md

@@ -0,0 +1,6 @@
+## Object Model: Reference Semantics
+
+_Skeleton descriptions are typeset in italic text,_
+_so please don't remove these descriptions when editing the topic._
+
+This topic is currently under construction and will soon be filled with information :)

sources/modules/object-model/value-semantics.md

@@ -0,0 +1,6 @@
+## Object Model: Value Semantics
+
+_Skeleton descriptions are typeset in italic text,_
+_so please don't remove these descriptions when editing the topic._
+
+This topic is currently under construction and will soon be filled with information :)

sources/modules/program-design/containers.md

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+## Program Design: Containers
+
+_Skeleton descriptions are typeset in italic text,_
+_so please don't remove these descriptions when editing the topic._
+
+This topic is currently under construction and will soon be filled with information :)

sources/modules/program-design/iterators.md

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+## Program Design: iterators {#it}
+
+_Skeleton descriptions are typeset in italic text,_
+_so please don't remove these descriptions when editing the topic._
+
+### Overview
+
+_Provides a short natural language abstract of the module’s contents._
+_Specifies the different levels of teaching._
+
+------------------------------------------------------------------------
+Level             Objective
+----------------- ------------------------------------------------------
+Foundational      Using iterators
+
+Main              Writing iterators
+
+Advanced          ---
+
+------------------------------------------------------------------------
+
+### Motivation
+
+_Why is this important?_
+_Why do we want to learn/teach this topic?_
+
+Iterators provide a generic interface between algorithms and containers.
+The container defines the iteration over its data.
+Therefore, the algorithm does neither need to know about the iteration nor the concrete data types that are stored in the container.
+This way, algorithms can be implemented in a generic way without detailed knowledge of the containers they operate on, and the containers can be written without predetermining what algorithms should be available for it.
+
+### Topic introduction
+
+_Very brief introduction to the topic._
+
+### Foundational: Using iterators {#it-found}
+
+#### Background/Required Knowledge
+
+A student:
+* containers [[Program Design: Containers - Foundational]][1]
+* for loops
+* [Maybe] [[Object Model: Value Semantics - Foundational]][2][[Object Model: Reference Semantics - Foundational]][3] TODO: revisited after ref/value semantics 
+
+#### Student outcomes
+
+_A list of things "a student should be able to" after the curriculum._
+_The next word should be an action word and testable in an exam._
+_Max 5 items._
+
+A student should be able to:
+
+1. write a for loop using iterators (not just range-based for).
+2. use the canonical iterator operations (begin/end, dereference, etc.).
+3. use the appropriate operations with regard to the iterators category.
+4. show examples where iterators are invalidated by operations on a container.
+5. demonstrate how iterators provide an abstraction between the operation and the underlying data structure.
+
+#### Caveats
+
+_This section mentions subtle points to understand, like anything resulting in
+implementation-defined, unspecified, or undefined behavior._
+
+* Dangling iterators (i.e., having an iterator to a no longer valid container)
+* `end()` marks the position after the last element and, by that, is not dereferencable
+* When comparing iterators, both iterators need to belong to the same underlying data structure
+* Keep in mind that iterators do not guarantee that the underlying memory is contiguous.
+
+#### Points to cover
+
+_This section lists important details for each point._
+
+* Using standard iterators with iterator-based for loops
+    * Difference between value/reference semantics based for loops
+    * Explain connection to for-each
+* Basic iterator nomenclature and functionality
+    * begin/end
+    * Give an example of the typical for loop pattern `iter != end()`
+    * Dereferencing iterators
+    * Advancing iterators
+    * Iterator adapters for containers (e.g., `back_inserter`)
+* Explain in a simple way the differences between different iterator notions
+    * For example, forward/backward/random access
+    * Defer a more detailed explanation of iterator categories to main
+* Give a brief introduction to iterator invalidation
+    * Defer a more detailed explanation to main
+* Explain the design idea behind iterators
+    * Iterators provide abstraction
+    * Iterators decouple accessing elements and iterating over a container from the actual container type
+    * Iterators store the iteration state (i.e., where you are in the container)
+
+
+### Main: Writing iterators {#it-main}
+
+#### Background/Required Knowledge
+
+#### Student outcomes
+
+A student should be able to:
+
+1. create an iterator based on an existing iterator and change its behavior.
+2. create an standard compliant iterator for a self written container.
+3. determine when an iterator is invalidated and write code accordingly.
+
+#### Caveats
+
+* Beware when using iterators in a multi-threaded environment as both the iterator and the data structure need to be correctly synchronized (see XYZ). TODO: find reference
+* Make sure that the implementation of the iterator offers at least the interface and guarantees that its category offers.
+
+
+#### Points to cover
+
+* When and how to defined internal/external iterators
+    * Iterator adapters (external)
+        * adds additional logic (e.g., reverse iterators)
+        * non-linear iterators (e.g., skip some number elements)
+    * API-extending iterators (external/internal)
+        * e.g., adding a new pre-order traversal iterator to a tree
+* Iterator invalidation
+    * Modifying the underlying data structure can invalidate an iterator
+        * Different types of containers have different iterator invalidation characteristics, even on similar methods (e.g., `vector.push_back` vs `list.insert`).
+        * Invalidation can be unpredictable (e.g., a `push_back` to a vector may but does not have to invalidate an iterator)
+        * Containers that don’t have stable addressing have the problem of iterator invalidation.
+    * The iterator should not outlive the container (lifetime)
+* Templates and iterators
+    * Iterator type interface (`value_type`, `pointer`, `reference`, `iterator_category`)
+    * To support different types of iterators algorithms often use template parameters for the concrete iterator type and only rely on the interface of an iterator (see topic [[Program Design: Algorithms - Main]][4])
+
+
+### Advanced
+
+_These are important topics that are not expected to be covered but provide
+guidance where one can continue to investigate this topic in more depth._
+
+[1]: ../program-design/containers.md
+[2]: ../object-model/value-semantics.md
+[3]: ../object-model/reference-semantics.md
+[4]: ../program-design/algorithms.md