Written 21 February 2024

Over the years I discover small pieces of cogent advice about programming and being a developer that I find useful.

This page tries to collect those thoughts - for my benefit and perhaps others. Email me if you have something good, I'll consider adding it. ;)

Code Design

Applying DRY: intrinsically vs. coincidentally similar code

In Uni I learned that you should NEVER have duplicated code. But in the workplace, I've learned from wise old devs and from firsthand experience that this is not always the case.

My philosophy is as follows: Refactor intrinsically similar code - not coincidentally similar.

Coincidentally similar code is likely to change and differentiate. If you preemptively pull both sets of logic out into a common function, you'll later have to create parameters for differences, and you'll dirty your previously clean code.

An example of this might be a plain text template function and an HTML template function. While the initial implementation of these two functions is the same, the HTML function will need to be able to escape certain characters in the future - if you've pulled out a common function, you'll need now need to add a boolean argument to switch between HTML or plain text (which is ugly).

Intrinsically similar code NEEDS to be put in a common function, however. If you don't do this, you risk a business rule being inconsistently implemented.

An example of this is formatting dates as strings. If you identify two separate pieces (or even one piece) of code which use an anonymous string like "DD/MM/YYYY" to format a date, that should be pulled out into a global constant or date utility function. If you don't do this, you risk someone changing one of the format strings (or adding another anonymous one somewhere) to "MM/DD/YYYY" - and you'll end up confusing/misinforming your users and potentially making the client liable.

Determining whether similarities are coincidental or intrinsic is a matter of interrogating your domain, which is an essential part of the job of a developer anyway.

Aim to minimize shit, not maximize perfection.

I think as a junior developer especially, ones desire with code design is to try and find the absolute perfect abstractions and algorithms, and to over-engineer solutions.

At least that's what I did as a junior. I would spend too much time trying to perfect rather unimportant aspects of the system, and be disheartened with the continuing existence of bad code in our codebase.

And then I decided to flip my perspective. Rather than trying to make good things better, I would try to make bad things less terrible.

So as an example: rather than trying to fine-tune a usecase that is already working okay, I will try to identify important parts of a system which are not working well or are of poor quality, and make a small improvement.

This is an acceptance of the fact that software is the product of flawed corporations and people. And once you accept that, you have achieved zen, and you can move on to being productive.

Design by contract

Source: The Pragmatic Programmer

Check that the input (and sometimes output) of important functions are sensible. This can be as simple as a few assert statements, e.g.

public sendSms(String cell) {
    assert PhoneValidationUtil.ValidNumber(cell);
   // ...

Do this instead of defensive programming, and apply selectively: put it on your core business logic for specific variables.

By doing this, you'll help minimize unexpected costly mistakes where bad data gets through to your business logic.

Test first, refactor second

Good tests allows you to delete code with confidence. Good tests are piercing acceptance or integrations tests which test the main happy paths of the program as well as known edge cases. Refactoring generally means deleting and rewriting code.

The lesson: write acceptance tests before doing serious refactoring.

Curt comments are good

Having the code describe itself is a wonderful, but terribly hubristic idea. Once you've written and reviewed a piece of code that nonetheless had a bug in it, you should abandon the silly notion that you can understand code just by looking at it. Good code has comments in it.

BUT you still shouldn't comment for the sake of it. Here I think are good opportunities for commenting:

  • The steps of a large usecase function. Moving those steps to helper functions can help too.
  • Any function or piece of code which is working around something; e.g. a badly designed external API.
  • Assumptions around the form of input which cannot be expressed clearly with types (though see Design by Contract).
  • Any code which is logically related but where the relationship cannot be enforced by the code (e.g. needing a struct definition to stay in sync between a client and repository package).
  • An overview for a complex or relatively alien algorithm.


Prioritize people over architecture

Comradery is the most vital resource on a software project. It is more important than having a good architecture or a clean, well designed codebase.

Consider two hypotheticals. In the first case you have a well-architected, clear, and performant system - but with a team that does not trust itself, struggles to make decisions, and which has endless bad arguments about all-manner of minutia.

Then consider a second case. The codebase is full of spaghetti code, takes hours to deploy, and is relatively unclear - but the team embraces its constituent members, people jump in and help each other at a moments notice, decisions are made dispassionately and quickly, and individuals are largely empowered to decide how to code their own tickets as they see fit.

My bet is that the first team is going to be relatively unproductive in real terms (that is, being slow to deliver the right business functionality) and the second team will conversely be strangely effective. And the second team will be able to pragmatically refactor its system over time, whereas the first team will lack the openness to discuss and address real arising problems with their system.

Corollary #1: Major review comments are for broken code only

Don't make major, blocking code review comments if it is a difference of opinion, even if you are only doing so to force a discussion. I would even say you shouldn't make a major comment if something is violating the architecture, but still works.

Major comments should only be used if there is a bug that will cause business requirements to fail.

This is based on the ideas of comradery being key, the architecture of a system being a living thing, and that people should be empowered to do their work as they see fit (provided their solution works).

You can use minor comments though. Make it clear to the team that your nits are purely optional and they need not even be read.

I'm quite a rigorous reviewer, and this balance means I generally give 1 or two major comments and a dozen (sometimes several dozen) minors. I find that 90% of the time the reviewee will happily correct all the majors and most of the minors without any argument. Thats fine with me.


Implementation checks

Go has structural typing, so a type implements an interface merely by defining the same methods on itself.

While this can be useful for abstracting external types, it is often nice to be able to check at compile time that a type implements an interface.

A nice pattern I've seen for this is to assign an unnamed global variable of the interface type to an implementation instance, e.g.

type Hashable interface {
    Hash() []byte

type BasicThingy string
type StructThingy struct{}

// Implementation checks:
var _ Hashable = (BasicThingy)("")
var _ Hashable = &StructThingy{}

Here we check that BasicThingy and *StructThingy implement Hashable. If they don't, the compiler will generate a nice error message pointing at the assignment. For this reason, it is nice to put this assignment next to the implementation type declaration.

You don't need a dependency injection library

If you follow the Service pattern from DDD, then you'll have a number of services which transitively depend on each other. Typically, you'll use some dependency injection container or wiring library to have these services be connected upon startup.

But there's no reason you can't do this wiring yourself:

func main() {
    server := Wire()
func Wire() *http.Server {
    cfgProvider := config.NewProvider()
    svc := usecase.NewService(cfgProvider)
    return http.NewServer(cfgProvider, svc)


  • You don't need to depend on an external library
  • If it compiles then you know everything is wired
  • You can have custom Wire functions which e.g. substitute external client services with mock versions for integration tests.

It is very convenient for small projects.


Tool check and install

Often as part of your Makefile, you'll have directives which run dev tools to do things like lint your code, generate mocks, etc. What you may not be aware of is that - provided your dev tool can be installed via the shell - you can automate the installation of these tools when the directives are run for the first time. This makes it trivial for new starters on the repo to get up and going.

Here's an example for a Go tool:

GOBIN := $(shell go env GOPATH)/bin

inspect: $(GOBIN)/golangci-lint
	$(GOBIN)/golangci-lint run
	$(MAKE) install-golangci-lint
	curl -sSfL | sh -s -- -b $(GOBIN) v1.46.2
	rm -rf ./v1.46.2

If you run inspect, Make will check if a file at $(GOBIN)/golangci-lint exists. If it does not, the associated directive will be executed, which then leads to the install directive being executed, and finally whatever shell commands are needed to install the program are run.

Another benefit of this abstraction is that if you update the tool, you can just advise the team to run make install-golangci-lint manually.