attribute: add String method to Value and KeyValue #7812

bboreham · 2026-01-20T14:14:15Z

This gives nicer results when you pass one to fmt.Println, for example.

Disclosure: Claude wrote the tests for me. I deleted about a third of the cases it came up with as uninteresting.

This gives nicer results when you pass one to fmt.Println, for example. Signed-off-by: Bryan Boreham <[email protected]>

codecov · 2026-01-20T14:17:12Z

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.0%. Comparing base (b1e7bde) to head (f1e0756).

Files with missing lines	Patch %	Lines
attribute/value.go	50.0%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #7812     +/-   ##
=======================================
- Coverage   86.1%   86.0%   -0.1%     
=======================================
  Files        302     302             
  Lines      22046   22050      +4     
=======================================
- Hits       18991   18977     -14     
+ Misses      2675    2673      -2     
- Partials     380     400     +20

Files with missing lines	Coverage Δ
attribute/kv.go	`84.6% <100.0%> (-15.4%)`	⬇️
attribute/value.go	`82.4% <50.0%> (-10.3%)`	⬇️

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

bboreham · 2026-01-20T14:16:35Z

attribute/kv_test.go

+		{
+			name: "string with spaces",
+			kv:   attribute.String("key", "hello world"),
+			want: "{key:hello world}",


I find it surprising that strings are not quoted, especially with embedded spaces like here.
But this is what Value.Emit() did, so leaving this here for comment.

bboreham · 2026-01-20T14:17:45Z

attribute/kv_test.go

+		{
+			name: "invalid/uninitialized KeyValue",
+			kv:   attribute.KeyValue{},
+			want: "{:unknown}",


Maybe this should print something clearer?
Originally I wanted this for debugging purposes, so exactly what is in the object may be important.

I propose <invalid>.

bboreham · 2026-01-20T14:21:28Z

attribute/value_test.go

+		{
+			name:  "bool slice",
+			value: attribute.BoolSliceValue([]bool{true, false, true}),
+			want:  "[true false true]",


Also it was surprising to me that this one has no commas, while the int, float and string slices do.

bboreham · 2026-01-20T14:26:44Z

I dispute the findings of the code coverage CI check. I added two functions which are completely covered by tests; how could this make coverage go down?

pellared · 2026-01-20T14:24:31Z

attribute/kv.go

+// String implements the Stringer interface, used when you pass an object to fmt.Println, etc.
+func (kv KeyValue) String() string {
+	return "{" + string(kv.Key) + ":" + kv.Value.String() + "}"
+}


Suggested change

// String implements the Stringer interface, used when you pass an object to fmt.Println, etc.

func (kv KeyValue) String() string {

return "{" + string(kv.Key) + ":" + kv.Value.String() + "}"

}

// String returns key-value pair as a string, formatted like "key:value".

//

// The returned string is meant for debugging;

// the string representation is not stable.

func (kv KeyValue) String() string {

return string(kv.Key) + ":" + kv.Value.String()

}

Why? To follow prior art https://pkg.go.dev/go.opentelemetry.io/otel/log#KeyValue.String (more: #5117).

pellared · 2026-01-20T14:24:59Z

CHANGELOG.md

 - Add `go.opentelemetry.io/otel/semconv/v1.39.0` package.
  The package contains semantic conventions from the `v1.39.0` version of the OpenTelemetry Semantic Conventions.
  See the [migration documentation](./semconv/v1.39.0/MIGRATION.md) for information on how to upgrade from `go.opentelemetry.io/otel/semconv/v1.38.0.`(#7783)
+- Add `String` method to `attribute.Value` and `KeyValue`. (#7812)


Suggested change

- Add `String` method to `attribute.Value` and `KeyValue`. (#7812)

- Add `String` method to `attribute.Value` and `KeyValue` in `go.opentelemetry.io/otel/attribute`. (#7812)

pellared · 2026-01-20T14:29:13Z

attribute/value.go

+// String implements the Stringer interface, used when you pass an object to fmt.Println, etc.
+// Do not confuse with AsString, which you should call if you know the value is of String type.


Suggested change

// String implements the Stringer interface, used when you pass an object to fmt.Println, etc.

// Do not confuse with AsString, which you should call if you know the value is of String type.

// String returns Value's value as a string, formatted like [fmt.Sprint].

//

// The returned string is meant for debugging;

// the string representation is not stable.

pellared · 2026-01-20T14:31:46Z

attribute/kv_test.go

+		{
+			name: "invalid/uninitialized KeyValue",
+			kv:   attribute.KeyValue{},
+			want: "{:unknown}",


I propose <invalid>.

pellared · 2026-01-20T14:32:33Z

attribute/value.go

+// String implements the Stringer interface, used when you pass an object to fmt.Println, etc.
+// Do not confuse with AsString, which you should call if you know the value is of String type.
+func (v Value) String() string {
+	return v.Emit()


Shouldn't we deprecate Emit so that users migrate to the new method?

Attribute: Add String method to Value and KeyValue

f1e0756

This gives nicer results when you pass one to fmt.Println, for example. Signed-off-by: Bryan Boreham <[email protected]>

bboreham requested review from MrAlias, XSAM, dashpole, dmathieu, flc1125 and pellared as code owners January 20, 2026 14:14

bboreham commented Jan 20, 2026

View reviewed changes

pellared reviewed Jan 20, 2026

View reviewed changes

pellared changed the title ~~Attribute: Add String method to Value and KeyValue~~ attribute: add String method to Value and KeyValue Jan 20, 2026

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attribute: add String method to Value and KeyValue #7812

attribute: add String method to Value and KeyValue #7812

bboreham commented Jan 20, 2026 •

edited

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	- Add `String` method to `attribute.Value` and `KeyValue`. (#7812)
	- Add `String` method to `attribute.Value` and `KeyValue` in `go.opentelemetry.io/otel/attribute`. (#7812)

		// String implements the Stringer interface, used when you pass an object to fmt.Println, etc.
		// Do not confuse with AsString, which you should call if you know the value is of String type.

-// String implements the Stringer interface, used when you pass an object to fmt.Println, etc.
-// Do not confuse with AsString, which you should call if you know the value is of String type.
+// String returns Value's value as a string, formatted like [fmt.Sprint].
+//
+// The returned string is meant for debugging;
+// the string representation is not stable.

attribute: add String method to Value and KeyValue #7812

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attribute: add String method to Value and KeyValue #7812

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bboreham commented Jan 20, 2026 •

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