How to pass array of counter values into RegisterCallback()

[karthi8185]

Hi,
I am using opentelemetry to export some customize data to otelcollector. Here my question is any possibility to pass the array arguments into RegisterCallback()

In the below code, instead of passing name1[0], name1[1], name1[2]... any possibility of send name1. Also, is there any api/method to resolve the type converstion. Since name1 data type is metric.Int64ObservableCounter but register to call back argument is metric.Observable.

var name1 []metric.Int64ObservableCounter
......
_, err = meter.RegisterCallback(
func(ctx context.Context, o metric.Observer) error {
o.ObserveInt64(name1[0], int64(getMetricValue(fullName1)))
o.ObserveInt64(name1[1], int64(getMetricValue(fullName2)))
o.ObserveInt64(name1[2], int64(getMetricValue(fullName3)))
o.ObserveInt64(name1[3], int64(getMetricValue(fullName4)))
return nil
},
name1[0],
name1[1],
name1[2],
name1[3],
)

kindly guide me.

[pellared]

is there any api/method to resolve the type converstion

No. But you can create a helper function yourself.

[karthi8185]

Can you pls explain a little bit more information about (steps), it's really helpful to understand.
Since I am new to Golang. So I will try it from my end.

[dmathieu]

Something like this, which is pure go, not otel specific?

var name1 []metric.Int64ObservableCounter
_, err = meter.RegisterCallback(
    func(ctx context.Context, o metric.Observer) error {
        for i, v := range name1 {
            // getMetricValue is a method which knows the value to return based on `i` and `v` (the index and value of the observable counters). The actual logic/arguments of that method depends on what you need to do
            o.ObserveInt64(v, int64(getMetricValue(i, v)))
        }
        return nil
    }, name1...,
)

[karthi8185]

@dmathieu my current code is similar to that.. But i am getting below error

cannot use name1 (variable of type []"go.opentelemetry.io/otel/metric".Int64ObservableCounter) as []"go.opentelemetry.io/otel/metric".Observable value in argument to meter.RegisterCallback

As per my understanding type mismatch for the second argument (name1 here).

func (m *meter) RegisterCallback(f metric.Callback, insts ...metric.Observable) (metric.Registration, error)

[dmathieu]

You're trying to pass a slice of Int64ObservableCounter (see the [] at the beginning of the type name). You need to pass a single attribute.
The ... I put in my example should turn the slice into arguments. See https://gobyexample.com/variadic-functions

[karthi8185]

Hi @dmathieu
I did the same and got that error during compilation.

cannot use name1 (variable of type []"go.opentelemetry.io/otel/metric".Int64ObservableCounter) as []"go.opentelemetry.io/otel/metric".Observable value in argument to meter.RegisterCallback

_, err = meter.RegisterCallback(
func(ctx context.Context, o metric.Observer) error {
o.ObserveInt64(name1[0], int64(getMetricValue(fullName1)))
o.ObserveInt64(name1[1], int64(getMetricValue(fullName2)))
o.ObserveInt64(name1[2], int64(getMetricValue(fullName3)))
o.ObserveInt64(name1[3], int64(getMetricValue(fullName4)))
return nil
},
name1...,
)

Please help on this.