Metric & Logging #

Go-optics provides the ability to collect metrics and to log the focused elements during the execution of an action.

Metrics #

Metrics can be collected for an optic by using the WithMetrics combinator. The signature of the optic is not altered but it will now report metrics to the given Metrics object. The following metrics are collected.

Example

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	data := []string{"alpha", "beta", "gamma", "delta"}

	sortStringSlice := Ordered(
		TraverseSlice[string](),
		OrderBy[string, string](
			Identity[string](),
		),
	)

	//Attach metrics to the sort
	var m Metrics
	sortStringSlice = WithMetrics(sortStringSlice, &m)

	res := MustGet(
		SliceOf(
			sortStringSlice,
			4,
		),
		data,
	)

	fmt.Println(res)
	fmt.Println(m)

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When printing the metrics their names are abbreviated to their initial letter.

In this example we see that 4 elements were focused, The source was accessed once, to iterate over the slice, no index lookups and no length gets were performed.

Ordered also publishes a custom metric "comparisons". This indicates how many comparisons were performed during the sort.

Custom Metrics #

Custom metrics can be published from your on own custom optics using the IncCustomMetric

Example

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	data := []string{"alpha", "beta", "gamma", "delta"}

	//custom optic that publishes the len(string) as a custom metric.
	stringLen := CombiGetter[Pure, Void, string, string, int, int](
		func(ctx context.Context, source string) (Void, int, error) {
			strLen := len(source)
			IncCustomMetric(ctx, "len", strLen)
			return Void{}, strLen, nil
		},
		IxMatchVoid(),
		ExprCustom("custom string len"),
	)

	//Attach metrics to the stringLen
	var m Metrics
	stringLen = WithMetrics(stringLen, &m)

	res := MustGet(
		SliceOf(
			Compose(
				TraverseSlice[string](),
				stringLen,
			),
			4,
		),
		data,
	)

	fmt.Println(res)
	fmt.Println(m)

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The custom optic increments the len metric for each string that it processes. The final metric is the total string length that was processed.

Logging #

Additional logging can be enabled for an individual optic using the WithLogging combinator. Like the WithMetrics combinator WithLogging doesn’t change the signature of the optic.

Example

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	data := []string{"alpha", "beta", "gamma", "delta"}

	sortStringSlice := Ordered(
		TraverseSlice[string](),
		OrderBy[string, string](
			Identity[string](),
		),
	)

	//Attach logging to the sort
	sortStringSlice = WithLogging(sortStringSlice)

	res := MustGet(
		SliceOf(
			sortStringSlice,
			4,
		),
		data,
	)

	fmt.Println("Result:", res)

Playground

Run

Note: in the playground the logging will be written to rhe browser log.