This example is almost the same as simple, except that it moves evaluation from run time into build time.
At run time, instead of using the Pkl evaluator, it reads the embedded bytes and unmarshals it into a config struct.
During the course of evaluation, pkl-go will spawn the pkl CLI as a child process in order to execute the entrypoint Pkl programs.
Typically, evaluation happens at runtime, where the pkl.Evaluator API is used to eval Pkl data into Go data.
However, it’s possible to move evaluation to build time, where the evaluated results are serialized into binary, then later unmarshaled.
This means that the Pkl CLI does not need to be available in the environment when running the application.
This approach is not feasible if:
-
The Go application should be evaluating Pkl modules at runtime (e.g. if you are building a tool that allows configuration through Pkl)
-
readorimportrequires access to runtime inputs (e.g.dbPassword = read("env:DATABASE_PASSWORD"), assuming thatDATABASE_PASSWORDis only set at runtime).
| Directory | Description |
|---|---|
|
Pkl configuration sources |
|
Generated Go sources from Pkl |
|
Embedded Pkl binary data |
|
Internal Go files |
|
Server entrypoint |
To generate new Pkl sources for the AppConfig module, first install the Go code generator:
go install github.com/apple/pkl-go/cmd/pkl-gen-go@latestWith that installed, generate Go sources via:
pkl-gen-go pkl/AppConfig.pklThe code generator detects that the Go package for AppConfig is
github.com/apple/pkl-go-examples/simple/gen/appconfig, and the Go module
name is github.com/apple/pkl-go-examples (via the go.mod file), and
therefore places generated sources in gen/appconfig.
To generate config data, run go run cmd/internal/generate-pkl-data.
Alternatively, run go generate ./…, which will run both codegen and generate msgpack data.
First, follow the steps to generate config data.
go run cmd/main.goAlternatively, replace go run with go build, and start the resulting executable.