Performance improvements for attribute value AsStringSlice, AsFloat64Slice, AsInt64Slice, AsBoolSlice (#6011)

Good day,

This PR changes As[Bool|Int64|Float64|String]Slice to use a little less
reflection.

The benchstat result of this is as follows.
```
goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/internal/attribute
cpu: AMD Ryzen 7 Pro 7735U with Radeon Graphics     
                  │   org.txt    │               new.txt                │
                  │    sec/op    │    sec/op     vs base                │
AsFloat64Slice-16   373.3n ± 41%   181.0n ± 42%  -51.51% (p=0.000 n=10)

                  │  org.txt   │              new.txt               │
                  │    B/op    │    B/op     vs base                │
AsFloat64Slice-16   64.00 ± 0%   40.00 ± 0%  -37.50% (p=0.000 n=10)

                  │  org.txt   │              new.txt               │
                  │ allocs/op  │ allocs/op   vs base                │
AsFloat64Slice-16   3.000 ± 0%   2.000 ± 0%  -33.33% (p=0.000 n=10)
```

---------

Co-authored-by: Damien Mathieu <42@dmathieu.com>

CHANGELOG.md

@@ -19,6 +19,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Propagate non-retryable error messages to client in `go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#5929)
 - Propagate non-retryable error messages to client in `go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`. (#5929)
 - Propagate non-retryable error messages to client in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#5929)
+- Performance improvements for attribute value `AsStringSlice`, `AsFloat64Slice`, `AsInt64Slice`, `AsBoolSlice`. (#6011)
 
 ### Fixed
 

internal/attribute/attribute.go

@@ -49,12 +49,11 @@ func AsBoolSlice(v interface{}) []bool {
 	if rv.Type().Kind() != reflect.Array {
 		return nil
 	}
-	var zero bool
-	correctLen := rv.Len()
-	correctType := reflect.ArrayOf(correctLen, reflect.TypeOf(zero))
-	cpy := reflect.New(correctType)
-	_ = reflect.Copy(cpy.Elem(), rv)
-	return cpy.Elem().Slice(0, correctLen).Interface().([]bool)
+	cpy := make([]bool, rv.Len())
+	if len(cpy) > 0 {
+		_ = reflect.Copy(reflect.ValueOf(cpy), rv)
+	}
+	return cpy
 }
 
 // AsInt64Slice converts an int64 array into a slice into with same elements as array.
@@ -63,12 +62,11 @@ func AsInt64Slice(v interface{}) []int64 {
 	if rv.Type().Kind() != reflect.Array {
 		return nil
 	}
-	var zero int64
-	correctLen := rv.Len()
-	correctType := reflect.ArrayOf(correctLen, reflect.TypeOf(zero))
-	cpy := reflect.New(correctType)
-	_ = reflect.Copy(cpy.Elem(), rv)
-	return cpy.Elem().Slice(0, correctLen).Interface().([]int64)
+	cpy := make([]int64, rv.Len())
+	if len(cpy) > 0 {
+		_ = reflect.Copy(reflect.ValueOf(cpy), rv)
+	}
+	return cpy
 }
 
 // AsFloat64Slice converts a float64 array into a slice into with same elements as array.
@@ -77,12 +75,11 @@ func AsFloat64Slice(v interface{}) []float64 {
 	if rv.Type().Kind() != reflect.Array {
 		return nil
 	}
-	var zero float64
-	correctLen := rv.Len()
-	correctType := reflect.ArrayOf(correctLen, reflect.TypeOf(zero))
-	cpy := reflect.New(correctType)
-	_ = reflect.Copy(cpy.Elem(), rv)
-	return cpy.Elem().Slice(0, correctLen).Interface().([]float64)
+	cpy := make([]float64, rv.Len())
+	if len(cpy) > 0 {
+		_ = reflect.Copy(reflect.ValueOf(cpy), rv)
+	}
+	return cpy
 }
 
 // AsStringSlice converts a string array into a slice into with same elements as array.
@@ -91,10 +88,9 @@ func AsStringSlice(v interface{}) []string {
 	if rv.Type().Kind() != reflect.Array {
 		return nil
 	}
-	var zero string
-	correctLen := rv.Len()
-	correctType := reflect.ArrayOf(correctLen, reflect.TypeOf(zero))
-	cpy := reflect.New(correctType)
-	_ = reflect.Copy(cpy.Elem(), rv)
-	return cpy.Elem().Slice(0, correctLen).Interface().([]string)
+	cpy := make([]string, rv.Len())
+	if len(cpy) > 0 {
+		_ = reflect.Copy(reflect.ValueOf(cpy), rv)
+	}
+	return cpy
 }

internal/attribute/attribute_test.go

@@ -133,3 +133,13 @@ func BenchmarkStringSliceValue(b *testing.B) {
 		sync = StringSliceValue(s)
 	}
 }
+
+func BenchmarkAsFloat64Slice(b *testing.B) {
+	b.ReportAllocs()
+	var in interface{} = [2]float64{1, 2.3}
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		sync = AsFloat64Slice(in)
+	}
+}