The Go SDK documentation on Activities contains this sentence:
The result value can be either a basic type or a struct with the only requirement being that it is serializable.
Would it be possible to add a code sample to temporal-go-examples showing how to use a struct as the argument type to an activity and a return type from an activity?
Should one use the struct by value or by reference (pointer)? I might be talking rubbish here as I don’t have a lot of Go experience, which makes it all the more important to add such a code example.
1 Like
maxim
July 8, 2020, 3:27pm
2
We don’t have a simple example to demonstrate structure as an argument or result of an activity. But Particle Swarm Optimization sample does use structures this way .
The function signature of the activity has the Particle struct type as the return type rather than a pointer to the struct:
var rng *rand.Rand
// This is registration process where you register all your activity handlers.
func init() {
// initialize the RNG
// WARNING: the randomness of activity scheduling with multiple workers makes random number generation truly random and not repeatable in debugging
// worker.ReplayWorkflowHistoryFromJSONFile should be used to troubleshoot a specific workflow failure.
rng = rand.New(rand.NewSource(time.Now().UnixNano()))
}
func InitParticleActivity(ctx context.Context, swarm Swarm) (Particle, error) {
logger := activity.GetLogger(ctx)
logger.Info("initParticleActivity started.")
particle := NewParticle(&swarm, rng)
particle.UpdateFitness(&swarm)
return *particle, nil
}
func UpdateParticleActivity(ctx context.Context, swarm Swarm, particleIdx int) (Particle, error) {
This means I can’t write return nil, err in case there is an intermediate error to return. Can I also have it typed with a (*Particle, error)?
maxim
July 8, 2020, 6:31pm
4
I changed the activity code to the following and it worked:
err := workflow.ExecuteActivity(ctx, InitParticleActivityName, &swarm).Get(ctx, &particle)
func InitParticleActivity(ctx context.Context, swarm *Swarm) (*Particle, error) {
logger := activity.GetLogger(ctx)
logger.Info("initParticleActivity started.")
particle := NewParticle(swarm, rng)
particle.UpdateFitness(swarm)
return particle, nil
}
1 Like
mvp
March 24, 2022, 4:00pm
5
Re-asking part of the original question. Sorry if it has somehow been answered already.
This means I can’t write return nil, err in case there is an intermediate error to return
Your example above shows returning a pointer to a struct from an activity. But, in the workflow, how do I get nil or the struct ?
For example, the following code doesn’t work in the workflow.
var particle *Particle
err := workflow.ExecuteActivity(ctx, InitParticleActivityName, &swarm).Get(ctx, particle)
if particle == nil {
// do something
} else {
// do something else
}
The following works, but I can’t check whether the return value was nil.
var particle Particle
err := workflow.ExecuteActivity(ctx, InitParticleActivityName, &swarm).Get(ctx, &particle)
For anything you want to decode into a value, you can pass a pointer for it to see if it was nil. So if you return *Particle from the activity, you can pass a **Particle into the Get call. Try changing .Get(ctx, particle) to .Get(ctx, &particle) in your first set of code there.
1 Like
mvp
March 24, 2022, 4:28pm
7
Hi @Chad_Retz , that works. Thank you so much.