OOP345 - Workshop 4 - Solved

 Templates

In this workshop, you design and code a couple of class templates and test them on different instantiations.



## Learning Outcomes

Upon successful completion of this workshop, you will have demonstrated the abilities to:

- design and code a class template
- template a class variable
- specialize a class template for a particular type
- instantiate a template class
- specialize a member function of a class template to process a particular type
- derivate a template class from another template class







## *In-Lab*

This workshop consists of three modules:
- `w3` (supplied)
- `List`
- `LVPair`

Enclose all your source code within the `sdds` namespace and include the necessary guards in each header file.



### `w3` Module (supplied)


**Do not modify this module!**  Look at the code and make sure you understand it.



### `List` Module

This module defines a class template for a collection of elements of any data type (for example, a list of `int`, or a list `Student`, etc.)

Design and code a class template named `List` for managing a statically allocated array of any datatype.  The template parameters in order of their specification are:

- `T`: the type of any element in the array
- `N`: the maximum number of elements in the array (an integer without sign)

Your design should be able to distinguish between
- the capacity of the array (`N`)
- the number of elements added to the list. Initially the list is empty.

***Public Members***
- `size_t size() const`: returns the number of elements in the list
- `const T& operator[](size_t i) const`: returns the element at index `i` (assume the parameter is valid).
- `void operator+=(const T& tt)`: if the list didn't reach the capacity, add a copy of the parameter to the array. Otherwise, do nothing.



### `LVPair` Module


Design and code a class template named `LVPair` for managing a *label-value* pair. The template parameters identify the types of the label and value objects that constitute an `LVPair` object:
- `L`: the type of the label
- `V`: the type of the value

***Public Members***
- `LVPair()`: sets the object in an empty state
- `LVPair(const L& aa, const V& bb)`: copies the values received in the parameters into the instance variables.
- `const L& key() const`: returns the **key** component of the pair
- `const V& value() const`: returns the **value** component of the pair
- `void display(std::ostream& os) const`: inserts into the parameter the stored values in the following format
```
LABEL : VALUE<endl>
```


***Free Helpers***
- `std::ostream& operator<<(std::ostream& os, const sdds::LVPair<L, V>& pair)`: calls the function `LVPair<L, V>::display()` to insert a pair into the stream.



### Sample Output

When the program is started with the command (the file `sales.txt` is provided):
```
w3.exe sales.txt
```
the output should look like:
```
Command Line:
--------------------------
  1: w3.exe
  2: sales.txt
--------------------------

Detail Ticket Sales
--------------------------
Student : 25
Adult : 13
Student : 12
Adult : 6
Student : 5
Adult : 15
```




## *At-Home*

The *at-home* part of this workshop upgrades your *in-lab* solution to include
- alignment of the label and value output in pretty columnar format
- accumulation of the values stored in a `List`, for a specified label

To implement each upgrade, you will derive a templated class from your original templated class (one derived class from `List` and one derived class from `LVPair`) and specialize the class derived from `LVPair` as described below.



### `LVPair` Module

The `LVPair` module must be upgraded to include both summation and label alignment functionality.

Modify the function `display()` in the class `LVPair` to enable polymorphism on it (make it `virtual`). This is the only change that you need to make to your original template.

Add to this module a class template named `SummableLVPair` to manage the summation and pretty displaying of labeled values.

This class is derived from `LVPair<L, V>`, and receives 2 template parameters:
- `L`: the type of the label
- `V`: the type of the value


***Static Private Members for `SummableLVPair`***
- an object of type `V` that holds the initial value for starting a summation. The initial value depends on the type of the value in the label-value pair and will be defined separately.
- a variable of type `size_t` that holds the minimum field width for pretty columnar output of label-value pairs (initialize it with 0). This is the minimum number of characters needed to display any of the labels in a set of labels.

  This value must be updated every time a new pair is added to the collection.



***Static Public Members for `SummableLVPair`***

- `static const V& getInitialValue()`: return the initital value stored.



***Public Members for `SummableLVPair`***

- default constructor

- `SummableLVPair(const L& lbl, const V& val)`: stores the pair in the collection, and updates the field width if necessary.
  This functions assumes that the type `L` supports a function named `size()` that returns the number of characters required to display `lbl`.

- `V sum(const L& lbl, const V& val) const`:
  - If the label of the pair stored in the current instance is `lbl`, then add the value of the pair and `val` together and return the result. Use `+` for addition.
  - Otherwise, return `val`.

- `void display(std::ostream& os) const`: set the alignment to left and the field width and then call `display()` from the parent class. At the end, restore the alignment to right.



***Specializations***

- for `SummableLVPair<std::string, std::string>`, the initial value for summation should be set to empty string (`""`).

- for `SummableLVPair<std::string, int>`, the initial value for summation should be set to 0.

- for `SummableLVPair<std::string, std::string>`, the function `sum()` should concatenate the values stored using `, ` as separator (use operator `+` to concatenate strings).




### `List` Module

The template class `List` doesn't need any change.

Add to this module another **template** class called `LVList`, that can manage a collection of *summable* elements.

This class is derived from `List<T, N>`, and receives 4 template parameters:
- `L`: the type of a label
- `V`: the type summation value
- `T`: the type of any element in the collection
- `N`: the maximum number of elements in the collection (an integer without sign)

In this design, `summable` elements are objects of a type that supports the operation `V sum(const L& l, const V& v)`.


***Public Members for `LVList`***
- `V accumulate(const L& label) const`: this function accumulates all the values stored in the list that have the label `label` into a local object of type `V`.

  - get the initial value from the type `T` and store it into a local variable of type `V`: this is the accumulator.
    In this design, the type `T` must have a static member called `getInitialValue()`.

  - iterate over the collection and call the function `sum()` for each item (use the overloaded `operator[]` to access the item at index `i`). Store the result of `sum()` into the accumulator.

  - return the accumulator to the client.


Once the implementation of this module is complete, if you attempt to instantiate the class `LVList` using a type `T` that doesn't support the `sum()` and `getInitialValue()` operations, you will receive compilation errors **for that specific instantiation**.




### Sample Output

When the program is started with the command:
```
w3.exe products.txt sales.txt
```
the output should look like:
```
Command Line:
--------------------------
  1: w3.exe
  2: products.txt
  3: sales.txt
--------------------------

Individual Index Entries
--------------------------
Grocerries  : tomatoes
Electronics : computer
Tools       : hammer
Grocerries  : lettuce
Grocerries  : potatoes
Electronics : Multimedia_Player
Electronics : HDD
Grocerries  : meat
Tools       : jigsaw

Collated Index Entries
--------------------------
      Tools: hammer, jigsaw
 Grocerries: tomatoes, lettuce, potatoes, meat
 Electrnics:
Electronics: computer, Multimedia_Player, HDD

Detail Ticket Sales
--------------------------
Student : 25
Adult   : 13
Student : 12
Adult   : 6
Student : 5
Adult   : 15

Summary of Ticket Sales
--------------------------
Student Tickets =   86.10
Adult Tickets   =  110.50
```



### Reflection

Study your final solution, reread the related parts of the course notes, and make sure that you have understood the concepts covered by this workshop. **This should take no less than 30 minutes of your time.**

Create a **text** file named `reflect.txt` that contains your detailed description of the topics that you have learned in completing this particular workshop and mention any issues that caused you difficulty and how you solved them. Include in your explanation—**but do not limit it to**—the following points:
- the reason for specializing the `sum()` member function.
- the reason for specializing the initial value for a summation.
- the reason for defining the class variable outside the class definition.



#### Quiz Reflection

Add a section to `reflect.txt` called **Quiz X Reflection**. Replace the **X** with the number of the last quiz that you received and list all questions that you answered incorrectly.

Then for each incorrectly answered question write your mistake and the correct answer to that question. If you have missed the last quiz, then write all the questions and their answers.