This in-class live coding exercise is an example of a very basic blog website in Rails, using a linked list to store each post's comments.
The goal with this exercise is to build an implementation of a linked list data structure by explicitly managing the references that ultimately form the links in between each node in the list.
In general, references are any piece of data that allows a computer program to access another piece of data. For example your social security number might be a reference to your tax information in an IRS database. However, the floating point decimal number 5.3 is not a reference because it directly IS the data.
There are two broad kinds of references: identifiers and locators.
Here are a few examples of both kinds of references, many of which you may be familiar with already:
| Identifier reference | Locator reference |
|---|---|
| Social Security Number | Street Address |
| ISBN | Latitude/Longitude |
SQL table id column |
Memory Address |
| URI | URL |
As we can see, references are used all over the place both in our computer systems and our formalized social systems.
References are often used because its not beneficial or possible to store a copy of the referenced data at each location where such a reference would be used. This might be due to constraints on data storage, but it might also be a result of how complicated it would be to update each copy when the data changes.