754: Dependencies

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Dependencies
The prereqs for CPSC 357, the class on package management, are CPSC 432, CPSC 357, and glibc2.5 or later.
Title text: The prereqs for CPSC 357, the class on package management, are CPSC 432, CPSC 357, and glibc2.5 or later.

[edit] Explanation

Ambox notice.png This explanation may be incomplete or incorrect: this explain is still a horror for non programmers.
If you can address this issue, please edit the page! Thanks.

One of the responsibilities of a compiler (a program that converts computer code to something the computer can actually read, as per 303: Compiling) is dependency resolution, the process of identifying what other components are necessary in order to construct a target component. Those other components may in turn may have their own requirements, all of which must also be satisfied.

On college campuses, course names indicate the department and level of a course. CPSC would be one way to express Computer Science classes, and course numbers in the 400 range would likely indicate a senior-level course.

The comic envisions a college computer science course (CPSC432) focusing on dependency resolution which has itself as a prerequisite. This dependency structure would send a naïve compiler into an infinite loop. In real life, the problem is solved by allowing an object to satisfy itself as a prerequisite. You see this, for example, every time you compile a recursive function.

The joke is that any student who successfully enrolls in the class already knows this solution because they must have employed it in order to get past the apparent infinite recursion in the class prerequisites.

Package management is a problem in software deployment similar to compiler dependency resolution, except that the dependencies are collections of files known as "packages".

The title text posits a course on package management which is dependent not only on itself (recursive dependency), but also on the course presented in the main comic, which has a higher course number. Package managers resolve self-dependencies in much the same way as compilers do, but a dependency from a lower-numbered package to a higher-numbered package is typically disallowed because it can create cycles in what is supposed to be a tree structure. glibc is a commonly-used package on Unix systems. Its inclusion as a course prerequisite blurs the line between the course material and the course itself.

[edit] Transcript

A portion of a page from an imaginary course catalog.
Page 3
[A table with four columns labeled Department, Course, Description, and Prereqs. Under 'Department' it reads, "computer science". Under 'course' it reads, "CPSC 432". Under 'Description' it reads, "Intermediate compiler design, with a focus on dependency resolution." Under 'Prereqs' it reads, "CPSC 432".]
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Discussion

Concurrent enrollment FTW 75.60.27.102 03:11, 29 March 2013 (UTC)

I'm a programmer so I'm ok with the explanation, but it seems too technical for non programmers. 108.162.212.196 02:22, 12 January 2014 (UTC)

In response to the programmer at 108.162.212.196: yes, it's probably too technical for non-programmers. But then again, so is the comic. It's a programming (or logic) joke. Unfortunately the level of knowledge required to 'get' some of Randall's humour can't always be reduced down to a simplistic lowest common denominator. 141.101.81.216 06:36, 24 February 2014 (UTC)

"Yes, Microsoft CRT 9.0 or later is acceptable. But you should probably think about getting MinGW, Cygwin, or just switch to Linux." (groan) 108.162.221.9 01:00, 17 April 2014 (UTC)

CPSC 432 lists itself as a prereq, not a coreq. A coreq can be satisfied by enrolling in the original course and the coreq course at the same time; however, prior completion of the course is required in the case of a prereq. So the dependency problem here cannot be solved by allowing a course to satisfy itself, and as a result, no one will be able to enroll in this course. The joke here is thus that the instructor of a course on dependency resolution created a dependency problem himself. --Troy0 (talk) 07:04, 17 August 2014 (UTC)
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