[chore] primitive slice, avoid allocation if enough space (#6061)

Signed-off-by: Bogdan <[email protected]>

Signed-off-by: Bogdan <[email protected]>

pdata/internal/cmd/pdatagen/internal/primitive_slice_structs.go

@@ -38,12 +38,12 @@ func New${structName}() ${structName} {
 
 // AsRaw returns a copy of the []${itemType} slice.
 func (ms ${structName}) AsRaw() []${itemType} {
-	return copy${structName}(*ms.getOrig())
+	return copy${structName}(nil, *ms.getOrig())
 }
 
 // FromRaw copies raw []${itemType} into the slice ${structName}.
 func (ms ${structName}) FromRaw(val []${itemType}) {
-	*ms.getOrig() = copy${structName}(val)
+	*ms.getOrig() = copy${structName}(*ms.getOrig(), val)
 }
 
 // Len returns length of the []${itemType} slice value.
@@ -69,17 +69,12 @@ func (ms ${structName}) MoveTo(dest ${structName}) {
 
 // CopyTo copies ${structName} to another instance.
 func (ms ${structName}) CopyTo(dest ${structName}) {
-	*dest.getOrig() = copy${structName}(*ms.getOrig())
+	*dest.getOrig() = copy${structName}(*dest.getOrig(), *ms.getOrig())
 }
 
-func copy${structName}(from []${itemType}) []${itemType} {
-	if len(from) == 0 {
-		return nil
-	}
-
-	to := make([]${itemType}, len(from))
-	copy(to, from)
-	return to
+func copy${structName}(dst, src []${itemType}) []${itemType} {
+	dst = dst[:0]
+	return append(dst, src...)
 }`
 
 const immutableSliceTestTemplate = `func TestNew${structName}(t *testing.T) {

pdata/pcommon/common.go

@@ -1046,7 +1046,7 @@ type ImmutableByteSlice = ByteSlice
 // NewImmutableByteSlice creates a new ByteSlice by copying the provided []byte slice.
 // Deprecated: [0.60.0] Use New{structName}() and {structName}.FromRaw([]byte) instead
 func NewImmutableByteSlice(from []byte) ByteSlice {
-	orig := copyByteSlice(from)
+	orig := copyByteSlice(nil, from)
 	return ByteSlice(internal.NewByteSlice(&orig))
 }
 
@@ -1056,7 +1056,7 @@ type ImmutableFloat64Slice = Float64Slice
 // NewImmutableFloat64Slice creates a new Float64Slice by copying the provided []float64 slice.
 // Deprecated: [0.60.0] Use New{structName}() and {structName}.FromRaw([]float64) instead
 func NewImmutableFloat64Slice(from []float64) Float64Slice {
-	orig := copyFloat64Slice(from)
+	orig := copyFloat64Slice(nil, from)
 	return Float64Slice(internal.NewFloat64Slice(&orig))
 }
 
@@ -1066,6 +1066,6 @@ type ImmutableUInt64Slice = UInt64Slice
 // NewImmutableUInt64Slice creates a new UInt64Slice by copying the provided []uint64 slice.
 // Deprecated: [0.60.0] Use New{structName}() and {structName}.FromRaw([]uint64) instead
 func NewImmutableUInt64Slice(from []uint64) UInt64Slice {
-	orig := copyUInt64Slice(from)
+	orig := copyUInt64Slice(nil, from)
 	return UInt64Slice(internal.NewUInt64Slice(&orig))
 }