“The boy put the box in the bag.”

Just to refresh your grade school English (which I had to do as well), take a brief look at the sentence diagramming article on wikipedia. Our sentence above boils down to:

Subject: “The boy”
Predicate & Direct object: “put the box”
Indirect object: “in the bag”

How would you represent that in code? Think about it for a second before continuing. So, here are the possibilities of how this could be written with a single method call:

// Subject-Oriented programming:
// "The boy put the box in the bag"
boy.PutIn(box, bag);

// Direct-object oriented programming:
// "The box was put in the bag by the boy"
box.PutIn(bag, boy);

// Indirect-object oriented programming:
// "The bag, to which was added a box, was done by the boy."  OR
// "A bag now has a box that was put there by the boy."
bag.AddTo(box, boy);

So, which is correct via the principles of OOP? What’s the correct place for the method that does the work? Is it on the Subject of the sentence? The Direct Object? Were you taught how to design this? (i.e. in school?)

In practice, method placement is one of the biggest factors in how maintainable & testable your code is, and code is rarely as simple as what I’ve shown above. How do you figure out where the right place for your methods are?

One code base where this was thought about a lot was in Python’s handling of string & list methods. The split() and join() methods in Python are both on the string type. In other words: The list type is rigid in that its methods contain no string-manipulation. This seems good at first until you read the code:

s = "Hello, world"
# Split the string into a list of "Hello" and "world":
l = s.split(',')
# Now, take that resulting list, and join it back together:
j = ','.join(l)

Wow, that last line looks weird! What’s going on there? We’re creating a temporary string “,” and then calling the join() method! Weird! For that last line, I would have much preferred to write:

j = l.join(',')

To be symmetric with the original splitting code, but to write things that way would place a string generating method “join()” on the list class, which also seems wrong.

The integration and instant feedback between test & code

The notion of “spec” (not “unittest”)

The spliraling nature of the way he writes the code.

Here’s the blog post with the embedded video, but the embedding size is too small to see what’s going on.

Here’s the direct link to the video on Vimeo, which won’t make too much sense unless you read the blog post first.

XML essentially is a programming language that allows users to customize the underlying format of their word-processing documents

It peeves me a lot when people refer to things like XML and HTML as “programming languages” because there’s no actual programming (i.e. control flow of execution and conditional statements, to start) involved in using them.  They’re document or data formats, and that’s it.  HTML is as much a programming language as a typewriter is a computer.

I hereby propose that we stop using the term “Programming Language” to refer to anything that’s not turing complete.

We can also ask google what it thinks about the matter…

perl -pi -e “s/foo/bar/g”

Is there a way to do this in Python and be as concise? That would be really nice, and would eliminate one more place where I end up using Perl and tearing my hair out every time.