Internets of Interest #7: Ian Cooper on Test Driven Development

As the tech lead on non SaaS product I spend a lot of my time worrying about testing. Specifically we have tests that cover code, but what is covering the tests? Tests are important to give you certainty that what your product says on the tin is what it will do when people take it home and unwrap it, but what’s backstopping the tests? Testing lets you refactor with impunity, but what if you want to refactor your tests?

This presentation by Ian Cooper takes a little while to get going but is worth persisting with. Cooper’s observations that the unit of the unit test is not a type, or a class, but the API–in Go terms, the public API of a package–was revelatory for me.

Bonus: Michael Feathers’ YOW ! 2016 presentation; Testing Patience.

Internets of Interest #4: Niall Murphy’s Polemic Against On-Call

The interaction between career development and on-call is actually really, really, bad. Bluntly, the profession takes on-call seriously, tries to be good at it, yet it is very very rare for this to be rewarded in any meaningful way. In 11 years at my previous employer, I never saw anyone get promoted for on-call performance.

Not once.

Internets of interest #2: John Ousterhout discusses a Philosophy of Software Design

Ousterhout’s opus is tearing up tech twitter at the moment. But for those outside the North American prime shipping service area, we’re shit out of luck until a digital version is available. Until then, here’s Ousterhout’s Google Tech talk:


Internets of interest #1: Brian Kernighan on the Elements of Programming Style

“It turns out that style matters in programming for the same reason that it matters in writing. It makes for better reading.”
— Douglas Crockford

I stumbled across this old (in internet years) presentation a few weeks ago and it’s been on high rotation since. If you can look past the recording difficulties (and the evacuation siren) this presentation is chock full of sound advice applicable to all programmers.


Maybe adding generics to Go IS about syntax after all

This is a short response to the recently announced Go 2 generics draft proposals

Update: This proposal is incomplete. It cannot replace two common use cases. The first is ensuring that several formal parameters are of the same type:

contract comparable(t T) {
        t > t

func max(type T comparable)(a, b T) T

Here a, and b must be the same parameterised type — my suggestion would only assert that they had at least the same contract.

Secondly the it would not be possible to parameterise the type of return values:

contract viaStrings(t To, f From) {
	var x string = f.String()

func SetViaStrings(type To, From viaStrings)(s []From) []To

Thanks to Ian Dawes and Sam Whited for their insight.


My lasting reaction to the Generics proposal is the proliferation of parenthesis in function declarations.

Although several of the Go team suggested that generics would probably be used sparingly, and the additional syntax would only be burden for the writer of the generic code, not the reader, I am sceptical that this long requested feature will be sufficiently niche as to be unnoticed by most Go developers.

It is true that type parameters can be inferred from their arguments, the declaration of generic functions and methods require a clumsy (type parameter declaration in place of the more common <T> syntaxes found in C++ and Java.

The reason for (type, it was explained to me, is Go is designed to be parsed without a symbol table. This rules out both <T> and [T] syntaxes as the parser needs ahead of time what kind of declaration a T is to avoid interpreting the angle or square braces as comparison or indexing operators respectively.

Contract as a superset of interfaces

The astute Roger Peppe quickly identified that contracts represent a superset of interfaces

Any behaviour you can express with an interface, you can do so and more, with a contract.

The remainder of this post are my suggestions for an alternative generic function declaration syntax that avoids add additional parenthesis by leveraging Roger’s observation.

Contract as a kind of type

The earlier Type Functions proposal showed that a type declaration can support a parameter. If this is correct, then the proposed contract declaration could be rewritten from

contract stringer(x T) {
        var s string = x.String()


type stringer(x T) contract {
	var s string = x.String()

This supports Roger’s observation that a contract is a superset of an interface. type stringer(x T) contract { ... } introduces a new contract type in the same way type stringer interface { ... }introduces a new interface type.

If you buy my argument that a contract is a kind of type is debatable, but if you’re prepared to take it on faith then the remainder of the syntax introduced in the generics proposal could be further simplified.

If contracts are types, use them as types

If a contract is an identifier then we can use a contract anywhere that a built-in type or interface is used. For example

func Stringify(type T stringer)(s []T) (ret []string) {
	for _, v := range s {
		ret = append(ret, v.String())
	return ret

Could be expressed as

func Stringify(s []stringer) (ret []string) {
	for _, v := range s {
		ret = append(ret, v.String())
	return ret

That is, in place of explicitly binding T to the contract stringer only for T to be referenced seven characters later, we bind the formal parameter s to a slice of stringer s directly. The similarity with the way this would previously be done with a stringer interface emphasises Roger’s observation.1

Unifying unknown type parameters

The first example in the design proposal introduces an unknown type parameter.

func Print(type T)(s []T) {
	for _, v := range s {

The operations on unknown types are limited, they are in some senses values that can only be read. Again drawing on Roger’s observation above, the syntax could potentially be expressed as:

func Print(s []contract{}) {
	for _, v := range s {

Or maybe even

type T contract {}

func Print(s []T) {
	for _, v := range s {

In essence the literal contract{} syntax defines an anonymous unknown type analogous to interface{}‘s anonymous interface type.


The great irony is, after years of my bloviation that “adding generics to Go has nothing to do with the syntax”2, it turns out that, actually, yes, the syntax is crucial.

Internets of interest #0: The future of Microprocessors

This weekend I’ve been freshening up the introductory material for a workshop that Francesc Campoy and I are teaching at GopherCon this month. As part of my research, these videos have been on high rotation.

The first video by Sophie Wilson, the designer of the first ARM chip from which both the company and the line of RISC microprocessors we know today were born.

The second presentation by John Hennessy of Computer Architecture: A Quantitative Approach fame is a reprisal of the 2017 Turing Award lecture he gave with his co-author David Patterson.

The theme of both presentations is the same; the end of Dennard scaling and the tremendous technical and economic challenges in bringing extreme UV lithography to the commercial processor production will cap the growth in processor performance to 2-3% per year for the foreseeable future.

Source: John Hennessy and David Patterson, Computer Architecture: A Quantitative Approach, 6/e. 2018

Both Wilson and Hennessy see the future of processor design as a gestalt of CPUs, GPUs, DSPs and VLIW architectures. Issue of adapting mainstream imperative programming languages to these architectures remains very much an open question.

Using Go modules with Travis CI

In my previous post I converted httpstat to use Go 1.11’s upcoming module support. In this post I continue to explore integrating Go modules into a continuous integration workflow via Travis CI.

Life in mixed mode

The first scenario is probably the most likely for existing Go projects, a library or application targeting Go 1.10 and Go 1.11. httpstat has an existing CI story–I’m using Travis CI for my examples, if you use something else, please blog about your experience–and I wanted to test against the current and development versions of Go.


The straddling of two worlds is best accomplished via the GO111MODULE environment variable. GO111MODULE dictates when the Go module behaviour will be preferred over the Go 1.5-1.10’s vendor/ directory behaviour. In Go 1.11 the Go module behaviour is disabled by default for packages within $GOPATH (this also includes the default $GOPATH introduced in Go1.8). Thus, without additional configuration, Go1.11 inside Travis CI will behave like Go 1.10.

In my previous post I chose the working directory ~/devel/httpstat to ensure I was not working within a $GOPATH workspace. However CI vendors have worked hard to make sure that their CI bots always check out of the branch under test inside a working $GOPATH.

Fortunately there is a simple workaround for this, add env GO111MODULE=on before any go buildor test invocations in your .travis.yml to force Go module behaviour and ignore any vendor/ directories that may be present inside your repo.1

language: go
  - 1.10.x
  - master

  - linux
  - osx

dist: trusty
sudo: false

install: true

  - env GO111MODULE=on go build 
  - env GO111MODULE=on go test

Creating a go.mod on the fly

You’ll note that I didn’t check in the go.mod module manifest I created in my previous post. This was initially an accident on my part, but one that turned out to be beneficial. By not checking in the go.mod file, the source of truth for dependencies remained httpstat’s Gopkg.toml file. When the call to env GO111MODULE=on go build executes on the Travis CI builder, the go tool converts my Gopkg.toml on the fly, then uses it to fetch dependencies before building.

$ env GO111MODULE=on go build
go: creating new go.mod: module
go: copying requirements from Gopkg.lock
go: finding v1.5.0
go: finding v0.0.0-20170922123423-429f518978ab
go: finding v0.0.0-20170922011244-0744d001aa84
go: finding v0.0.0-20170915090833-1cbadb444a80
go: finding v0.0.9
go: finding v0.0.3
go: downloading v1.5.0
go: downloading v0.0.9
go: downloading v0.0.3
go: downloading v0.0.0-20170922011244-0744d001aa84
go: downloading v0.0.0-20170915090833-1cbadb444a80

If you’re not using a dependency management tool that go mod knows how to convert from this advice may not work for you and you may have to maintain a go.mod manifest in parallel with you previous dependency management solution.

A clean slate

The second option I investigated, but ultimately did not pursue, was to treat the Travis CI builder, like my fresh Ubuntu 18.04 install, as a blank canvas. Rather than working around Travis CI’s attempts to check the branch out inside a working $GOPATH I experimented with treating the build as a C project2 then invoking gimme directly. This also required me to check in my go.mod file as without Travis’ language: go support, the checkout was not moved into a $GOPATH folder. The latter seems like a reasonable approach if your project doesn’t intend to be compatible with Go 1.10 or earlier.

language: c

  - linux
  - osx

dist: trusty
sudo: false

  - eval "$(curl -sL | GIMME_GO_VERSION=master bash)"

  - go build 
  - go test

You can see the output from this branch here.

Sadly when run in this mode gimme is unable to take advantage of the caching provided by the language: go environment and must build Go 1.11 from source, adding three to four minutes delay to the install phase of the build. Once Go 1.11 is released and gimme can source a binary distribution this will hopefully address the setup latency.

Ultimately this option may end up being redundant if GO111MODULE=on becomes the default behaviour in Go 1.12 and the location Travis places the checkout becomes immaterial.