Patterns

Good Resources

Testing code that uses goroutines

I’m using github.com/stretchr/testify/mock:

type SomeService struct {

}

func (ss *SomeService) SomeMethod(parameter string) {
	go doSomethingElse()
}

func doSomethingElse() {
  // some thing we want to do
}

type SomeServiceMock struct {
	mock.Mock
	wg sync.WaitGroup
}

func (ss *SomeServiceMock) SomeMethod(parameter string) {
	defer ss.wg.Done()
	ss.Called(parameter)
}

func TestSomething(t *testing.T) {
  someService := new(SomeServiceMock)
  someService.wg.Add(1)
  someService.On("SomeMethod", "someParameter").Return(nil).Times(1)

  // execute code that we want to test using the someService mock

  someService.wg.Wait()
  mock.AssertExpectationsForObjects(t, someService)
}

Convert float to string

s := fmt.Sprintf("%f", 123.456) // s == "123.456000"

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Interesting Posts

The Zen of Go

See the original source here

Each package fulfils a single purpose

A well designed Go package provides a single idea, a set of related behaviours. A good Go package starts by choosing a good name. Think of your package’s name as an elevator pitch to describe what it provides, using just one word.

Handle errors explicitly

Robust programs are composed from pieces that handle the failure cases before they pat themselves on the back. The verbosity of if err != nil { return err } is outweighed by the value of deliberately handling each failure condition at the point at which they occur. Panic and recover are not exceptions, they aren’t intended to be used that way.

Return early rather than nesting deeply

Every time you indent you add another precondition to the programmer’s stack consuming one of the 7 ±2 slots in their short term memory. Avoid control flow that requires deep indentation. Rather than nesting deeply, keep the success path to the left using guard clauses.

Leave concurrency to the caller

Let the caller choose if they want to run your library or function asynchronously, don’t force it on them. If your library uses concurrency it should do so transparently.

Before you launch a goroutine, know when it will stop

Goroutines own resources; locks, variables, memory, etc. The sure fire way to free those resources is to stop the owning goroutine.

Avoid package level state

Seek to be explicit, reduce coupling, and spooky action at a distance by providing the dependencies a type needs as fields on that type rather than using package variables.

Simplicity matters

Simplicity is not a synonym for unsophisticated. Simple doesn’t mean crude, it means readable and maintainable. When it is possible to choose, defer to the simpler solution.

Write tests to lock in the behaviour of your package’s API

Test first or test later, if you shoot for 100% test coverage or are happy with less, regardless your package’s API is your contract with its users. Tests are the guarantees that those contracts are written in. Make sure you test for the behaviour that users can observe and rely on.

If you think it’s slow, first prove it with a benchmark

So many crimes against maintainability are committed in the name of performance. Optimisation tears down abstractions, exposes internals, and couples tightly. If you’re choosing to shoulder that cost, ensure it is done for good reason.

Moderation is a virtue

Use goroutines, channels, locks, interfaces, embedding, in moderation.

Maintainability counts

Clarity, readability, simplicity, are all aspects of maintainability. Can the thing you worked hard to build be maintained after you’re gone? What can you do today to make it easier for those that come after you?