Skip to main content

Simple code: Contracts

Code works around contracts and contracts should be carefully thought and crafted.

What are contracts


A High abstraction level of contracts for code are API's. They define a interface that is basically a contract that the producer and consumer of the API agree to use to communicate with each other. Two common forms of API's are libraries that are used in code and external API's  that are used via HTTP, RPC etc.

When thinking in a bit deeper contracts consist firstly of functions, methods or external endpoints and secondly of data, more precisely on data models and data types within the models.
 

Defining contracts


Contracts should always be defined with careful thought. I've come accross few times to someone saying that "this is for intenal use only so it doesn't need to defined and/or documented as thoughtfully as a public API would be" but I disagree with that. The same care should be be given to internal and external contracts because the contracts are defined to used by other code and most likely by other developers. Contracts are a key incredient in developer experience.

Tests love contracts


Contracts also work as a base for testing whether it's unit, integration or acceptance testing they are all implemented against a some sort of contract. Without properly defined contracts testing would be nearly impossible because of all the possible variations a badly designed API would enable.

Formats of contracts


One incarnation of data model contracts are schemas. Those who have worked long enough in the industry can remember SOAP, XML Schemas and WSDL, after XML came JSON and *drum roll* JSON schemas that are probably most often seen in Open API specifications. Some of the newer formats for defining contracts for code are e.g. Apache Avro and Protobuf. 

They're all basically the same thing just defined in a bit different format and they all address the same issue of defining a contract of what the input and ouput data must look like and some of the definitions also define transport protocols.

Contracts appear in many ways and the trick is to understand that they are actually contracts. Not just some random bits of code that can be whipped together without a second thought but something that deserves attention.

Next part


In the next part I'll be writing about a special thing, immutability.

Labels:
Location: Espoo, Finland

Popular posts from this blog

Simple code: Readability

Readability, understandability, two key incredients of great code. Easier said than done, right? What one person finds easy to read and understand another one finds incomprehensible. This is especially true when programmers have different levels of understanding on various subjects e.g. object oriented vs. functional or Node.js vs. Java. Even though there are obvious differences between paradigms and programming ecosystems there are some common conventions and ways to lower the barrier. Different approaches It's natural that in programming things happen sequentally e.g. you can have a list of objects and you need to do various things to the list like filter some values out and count a sum of the remaining objects based on some property. With the given list const stories = [   {name: "authentication", points: 43},   {name: "profile page", points: 11},   {name: "shopping cart", points: 24},   {name: "shopping history", points: 15},   {name: &qu
Read more

Sharing to help myself

It's been a while since my last post but I have a good excuse. I've been in a new customer project (well new for me) for two months now and have absorbed a lot of new information on the technology stack and the project itself. This time I'll be sharing a short post about sharing code and how it can help the one who's sharing the code. I'll be giving a real life example of how it happened to me. My story Back when I was implementing first version of my simple-todo REST-service I used Scala and Play framework for the service and specs2 for testing the implementation. Since then I've done a few other implementations of the service but I've continued to use specs2 as a testing framework. I wrote about my implementation and shared the post through various services and as a result someone forked my work and gave me some pointers on how I could improve my tests. That someone was Eric Torreborre  the man behind specs2 framework. I didn't take his ref
Read more

Simple code: Immutability

Immutability is a special thing that in my mind deserves a short explanation and praise. If you're familiar with functional programming you surely recognice the concept of immutability because it's a key ingredient of the paradigm. In the world of object oriented programming it's not as used and as easy to use approach but there are ways to incorporate immutability to parts of the code and I strongly suggest you to do so. Quick intro to immutablity The basic idea of immutability is unchangeable data.  Lets take a example. We have a need to modify a object's property but because the object is immutable we can't just change value but instead we make a copy of the object and while making the copy we provide the new value for the copy. In code it looks something like this. val pencil = Product(name = "Pencil", category = "Office supply") val blackMarker = pencil.copy(name = "Black marker") The same idea can be applied in functions and metho
Read more