1. Distinguishing logic from data type
Generics
Distinguishing logic from data type
Copyright © Curt Hill

2. History 1950s 1960s 1970s 1980s 1990s Assemblers High level languages
FORTRAN, ALGOL, COBOL, BASIC, etc
1970s
Structured languages, C, Pascal
1980s
Object oriented languages
Smalltalk, C++ and others
1990s
Generics in C++ and Ada
Copyright © Curt Hill

3. Basic Idea
There are a number of functions and classes where the data type being used does not matter
Consider several screens of examples
Copyright © Curt Hill

4. Linked List Destructor
LinkedList::~LinkedList(){
if(root == NULL)
return;
// Walk the list deleting everything
LinkedNode * ptr = root;
while(ptr){ // != NULL) {
root = ptr;
ptr = ptr -> next;
delete root; }
root = NULL;
Copyright © Curt Hill

5. Questions What kind of data did the list carry?
Do not know and do not care
The logic is the same in all cases
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6. Linked List ToString wxString LinkedList::ToString (){
wxString result = "";
if(root == NULL)
return "Empty\n";
LinkedNode * ptr=root;
while (ptr) {
result = result << wxString("Key: ") << ptr->key << ", data: " << ptr->data << "\n";
ptr = ptr->next; }
return result;
Copyright © Curt Hill

7. Questions What kind of data is in key and data? We still do not know
We do know that the data is subject to being converted to a wsString with the put-to operator
This could be any primitive, a C-style string or a few objects
Copyright © Curt Hill

8. Linked List Find bool LinkedList::find(? k, ? & s){
LinkedNode * ptr = root;
while(ptr){
if(ptr->key == k){
s = ptr->data;
return true; }
ptr = ptr->next;
return false;
Copyright © Curt Hill

9. Questions What kind of data is in k, d, key and data?
We could know because it must be declared
We do know that the data is suitable for comparison and assignment
Copyright © Curt Hill

10. C++ Has the template feature to implement generics Consider the sort
The code is mostly the same regardless of whether an array of ints or an array of doubles is in view
Consider the linked list
The code is mostly the same regardless of whether the list carries strings or floats
Thus generics separate logic from data type
Copyright © Curt Hill

11. Templates The reserved word for these is template
This is usually followed by a parameter list: template <class TYPE> thing
class precedes the generic name of the type
TYPE is the generic type
The thing is a class or function
There may be multiple types as well
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12. More
An alternative to the class reserved word is the typename reserved word
This was introduced in a later C++ standard
This better signifies that the parameterizing type may be:
A class
A primitive type
Anything named by a typedef
This true regardless of whether class or typename is used
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13. Process First we will examine template functions
They are easier
Second we will consider template classes
Similar but somewhat more involved
Copyright © Curt Hill