[#211] netmap: Introduce ReplicaDescriptor method

* Make ReplicaNumberByIndex deprecated.
* Introduce ReplicaDescriptor method that access i-th replica directly.
* Introduce new getters for ReplicaDescriptor.

Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>

netmap/policy.go

@@ -139,6 +139,14 @@ func (r *ReplicaDescriptor) SetNumberOfObjects(c uint32) {
 	r.m.SetCount(c)
 }
 
+func (r ReplicaDescriptor) SetECDataCount(v uint32) {
+	r.m.SetECDataCount(v)
+}
+
+func (r ReplicaDescriptor) SetECParityCount(v uint32) {
+	r.m.SetECParityCount(v)
+}
+
 // NumberOfObjects returns number set using SetNumberOfObjects.
 //
 // Zero ReplicaDescriptor has zero number of objects.
@@ -146,6 +154,19 @@ func (r ReplicaDescriptor) NumberOfObjects() uint32 {
 	return r.m.GetCount()
 }
 
+func (r ReplicaDescriptor) GetECDataCount() uint32 {
+	return r.m.GetECDataCount()
+}
+
+func (r ReplicaDescriptor) GetECParityCount() uint32 {
+	return r.m.GetECParityCount()
+}
+
+// TotalECPartCount returns total sum of ECDataCount and ECParityCount.
+func (r ReplicaDescriptor) TotalECPartCount() uint32 {
+	return r.m.GetECDataCount() + r.m.GetECParityCount()
+}
+
 // SetSelectorName sets name of the related Selector.
 //
 // Zero ReplicaDescriptor references to the root bucket's selector: it contains
@@ -179,10 +200,19 @@ func (p PlacementPolicy) NumberOfReplicas() int {
 // descriptor. Index MUST be in range [0; NumberOfReplicas()).
 //
 // Zero PlacementPolicy has no replicas.
+//
+// Deprecated: Use PlacementPolicy.ReplicaDescriptor(int).NumberOfObjects() instead.
 func (p PlacementPolicy) ReplicaNumberByIndex(i int) uint32 {
 	return p.replicas[i].GetCount()
 }
 
+// ReplicaDescriptor returns i-th replica descriptor. Index MUST be in range [0; NumberOfReplicas()).
+func (p PlacementPolicy) ReplicaDescriptor(i int) ReplicaDescriptor {
+	return ReplicaDescriptor{
+		m: p.replicas[i],
+	}
+}
+
 // SetContainerBackupFactor sets container backup factor: it controls how deep
 // FrostFS will search for nodes alternatives to include into container's nodes subset.
 //