DoSomethingToThing(Thing n) vs Thing.DoSomething()

Question

What factors determine which approach is more appropriate?

Answer 1

I think both have their places.

You shouldn't simply use DoSomethingToThing(Thing n) just because you think "Functional programming is good". Likewise you shouldn't simply use Thing.DoSomething() because "Object Oriented programming is good".

I think it comes down to what you are trying to convey. Stop thinking about your code as a series of instructions, and start thinking about it like a paragraph or sentence of a story. Think about which parts are the most important from the point of view of the task at hand.

For example, if the part of the 'sentence' you would like to stress is the object, you should use the OO style.

Example:

fileHandle.close();

Most of the time when you're passing around file handles, the main thing you are thinking about is keeping track of the file it represents.

CounterExample:

string x = "Hello World";
submitHttpRequest( x );

In this case submitting the HTTP request is far more important than the string which is the body, so submitHttpRequst(x) is preferable to x.submitViaHttp()

Needless to say, these are not mutually exclusive. You'll probably actually have

networkConnection.submitHttpRequest(x)

in which you mix them both. The important thing is that you think about what parts are emphasized, and what you will be conveying to the future reader of the code.

Answer 2

To be object-oriented, tell, don't ask : http://www.pragmaticprogrammer.com/articles/tell-dont-ask.

So, Thing.DoSomething() rather than DoSomethingToThing(Thing n).

Answer 3

If you're dealing with internal state of a thing, Thing.DoSomething() makes more sense, because even if you change the internal representation of Thing, or how it works, the code talking to it doesn't have to change. If you're dealing with a collection of Things, or writing some utility methods, procedural-style DoSomethingToThing() might make more sense or be more straight-forward; but still, can usually be represented as a method on the object representing that collection: for instance

GetTotalPriceofThings();

vs

Cart.getTotal();

It really depends on how object oriented your code is.