GoFundamental.md

1. How to ask a project to depend on the latest commit of a dependency pkg?

go get github.com/someone/some_module@af044c0995fe

// e.g.
go get github.com/numaproj/numaflow-go@44ff06c

Reference: https://stackoverflow.com/questions/53682247/how-to-point-go-module-dependency-in-go-mod-to-a-latest-commit-in-a-repo

2. A trick to ensure an object implements an interface

Sometimes you see it at the top of a go file and you think: "Why do we put it on this line?" It's because we want to explicitly ensure this struct client is an implementation of the interface Client.

var _ Client = (*client)(nil)

3. How to upgrade Go version

https://github.com/numaproj/numaflow/pull/966/files

4. The flag library

Within container, we can use flag library to read input configurations from command line.

var prefixStr string
flag.StringVar(&prefixStr, "prefix", "test-payload-", "Prefix of the payload")
flag.Parse()
simpleSource := impl.NewSimpleSource(prefixStr)

On Numaflow template, we can declare container as follow:

image: quay.io/numaio/numaflow-go/source-simple-source:v0.5.2
args: ["--prefix=abc-"]

The UDSource will then use abc- instead of default test-payload-, as its message payload prefix.

5. The % sign

%d -> integer value

%f -> floating point

%s -> plain string

%v -> default format

%w -> Enabling WRAPPING errors

Wrapping an error with %w makes it available to errors.Is and errors.As: (More details in Working with Errors)

err := fmt.Errorf("access denied: %w", ErrPermission)
...
if errors.Is(err, ErrPermission) ...

6. go mod

# Start a new module
go mod init module_name
# Add dependency
go get
# clean up and ensure "go.sum" files are up-to-date
go mod tidy

7. How to create a library Golang repo

go mod init github.com/numaproj-contrib/numaflow-utils-go