diff --git a/RandBLAS/base.hh b/RandBLAS/base.hh
index 9eb2fdac..e6529898 100644
--- a/RandBLAS/base.hh
+++ b/RandBLAS/base.hh
@@ -376,6 +376,7 @@ concept SketchingOperator = requires(SKOP S) {
     { S.dist   }     -> SketchingDistribution;
     { S.seed_state } -> std::same_as<const typename SKOP::state_t&>;
     { S.next_state } -> std::same_as<const typename SKOP::state_t&>;
+    { S.own_memory } -> std::same_as<bool&>;
 };
 #else
 #define SketchingOperator typename
diff --git a/RandBLAS/sparse_data/coo_matrix.hh b/RandBLAS/sparse_data/coo_matrix.hh
index c02445a8..0a29e610 100644
--- a/RandBLAS/sparse_data/coo_matrix.hh
+++ b/RandBLAS/sparse_data/coo_matrix.hh
@@ -220,9 +220,9 @@ struct COOMatrix {
 
     ~COOMatrix() {
         if (this->own_memory) {
-            delete [] this->vals;
-            delete [] this->rows;
-            delete [] this->cols;
+            if (vals != nullptr) delete [] vals;
+            if (rows != nullptr) delete [] rows;
+            if (cols != nullptr) delete [] cols;
         }
     };
 
@@ -235,13 +235,16 @@ struct COOMatrix {
     void reserve(int64_t nnz) {
         randblas_require(this->_can_reserve);
         randblas_require(this->own_memory);
+        randblas_require(vals == nullptr);
+        randblas_require(rows == nullptr);
+        randblas_require(cols == nullptr);
         this->nnz = nnz;
         if (this->nnz > 0) {
-            this->vals = new T[nnz];
-            this->rows = new sint_t[nnz];
-            this->cols = new sint_t[nnz];
+            vals = new T[nnz];
+            rows = new sint_t[nnz];
+            cols = new sint_t[nnz];
         }
-        this->_can_reserve = false;
+        _can_reserve = false;
     }
 
     /////////////////////////////////////////////////////////////////////
diff --git a/RandBLAS/sparse_data/csc_matrix.hh b/RandBLAS/sparse_data/csc_matrix.hh
index d9c3119c..15933dbd 100644
--- a/RandBLAS/sparse_data/csc_matrix.hh
+++ b/RandBLAS/sparse_data/csc_matrix.hh
@@ -136,9 +136,9 @@ struct CSCMatrix {
 
     ~CSCMatrix() {
         if (this->own_memory) {
-            delete [] this->rowidxs;
-            delete [] this->colptr;
-            delete [] this->vals;
+            if (rowidxs != nullptr) delete [] rowidxs;
+            if (colptr  != nullptr) delete [] colptr;
+            if (vals    != nullptr) delete [] vals;
         }
     };
 
@@ -151,15 +151,18 @@ struct CSCMatrix {
     //
     // @endverbatim
     void reserve(int64_t nnz) {
-        randblas_require(this->_can_reserve);
-        randblas_require(this->own_memory);
-        this->colptr = new sint_t[this->n_cols + 1]{0};
+        randblas_require(_can_reserve);
+        randblas_require(own_memory);
+        if (colptr == nullptr)
+            colptr = new sint_t[n_cols + 1]{0};
         this->nnz = nnz;
-        if (this->nnz > 0) {
-            this->rowidxs = new sint_t[nnz]{0};
-            this->vals = new T[nnz]{0.0};
+        if (nnz > 0) {
+            randblas_require( rowidxs == nullptr );
+            randblas_require( vals    == nullptr );
+            rowidxs = new sint_t[nnz]{0};
+            vals = new T[nnz]{0.0};
         }
-        this->_can_reserve = false;
+        _can_reserve = false;
     };
 
     CSCMatrix(CSCMatrix<T, sint_t> &&other) 
diff --git a/RandBLAS/sparse_data/csr_matrix.hh b/RandBLAS/sparse_data/csr_matrix.hh
index e4f54339..2c3e328c 100644
--- a/RandBLAS/sparse_data/csr_matrix.hh
+++ b/RandBLAS/sparse_data/csr_matrix.hh
@@ -139,10 +139,10 @@ struct CSRMatrix {
     ) : CSRMatrix(n_rows, n_cols, nnz, vals, rowptr, colidxs, IndexBase::Zero) {};
 
     ~CSRMatrix() {
-        if (this->own_memory) {
-            delete [] this->rowptr;
-            delete [] this->colidxs;
-            delete [] this->vals;
+        if (own_memory) {
+            if (rowptr  != nullptr) delete [] rowptr;
+            if (colidxs != nullptr) delete [] colidxs;
+            if (vals    != nullptr) delete [] vals;
         }
     };
 
@@ -154,15 +154,18 @@ struct CSRMatrix {
     //
     // @endverbatim
     void reserve(int64_t nnz) {
-        randblas_require(this->_can_reserve);
-        randblas_require(this->own_memory);
-        this->rowptr = new sint_t[this->n_rows + 1]{0};
+        randblas_require(_can_reserve);
+        randblas_require(own_memory);
+        if (rowptr == nullptr) 
+            rowptr = new sint_t[n_rows + 1]{0};
         this->nnz = nnz;
-        if (this->nnz > 0) {
-            this->colidxs = new sint_t[nnz]{0};
-            this->vals = new T[nnz]{0.0};
+        if (nnz > 0) {
+            randblas_require(colidxs == nullptr);
+            randblas_require(vals    == nullptr);
+            colidxs = new sint_t[nnz]{0};
+            vals    = new T[nnz]{0.0};
         }
-        this->_can_reserve = false;
+        _can_reserve = false;
     };
 
     /////////////////////////////////////////////////////////////////////
diff --git a/RandBLAS/sparse_skops.hh b/RandBLAS/sparse_skops.hh
index 29bd538d..87ce97e7 100644
--- a/RandBLAS/sparse_skops.hh
+++ b/RandBLAS/sparse_skops.hh
@@ -360,13 +360,7 @@ struct SparseSkOp {
         seed_state(seed_state),
         next_state(compute_next_state(dist, seed_state)),
         n_rows(dist.n_rows),
-        n_cols(dist.n_cols)
-    {   // actual work
-        // int64_t nnz = dist.full_nnz;
-        // this->rows = new sint_t[nnz]{-1};
-        // this->cols = new sint_t[nnz]{-1};
-        // this->vals = new T[nnz]{0.0};
-    }
+        n_cols(dist.n_cols) { }
 
     /// --------------------------------------------------------------------------------
     /// **View constructor**. The arguments provided to this
@@ -399,7 +393,7 @@ struct SparseSkOp {
     SparseSkOp(SparseSkOp<T,RNG,sint_t> &&S
     ) : dist(S.dist), seed_state(S.seed_state), next_state(S.next_state),
         n_rows(dist.n_rows), n_cols(dist.n_cols), own_memory(S.own_memory),
-        rows(S.rows), cols(S.cols), vals(S.vals)
+        nnz(S.nnz), rows(S.rows), cols(S.cols), vals(S.vals)
     {
         S.rows = nullptr;
         S.cols = nullptr;
@@ -408,13 +402,10 @@ struct SparseSkOp {
 
     //  Destructor
     ~SparseSkOp() {
-        if (this->own_memory) {
-            if (this->rows != nullptr)
-                delete [] this->rows;
-            if (this->cols != nullptr)
-                delete [] this->cols;
-            if (this->vals != nullptr)
-                delete [] this->vals;
+        if (own_memory) {
+            if (rows != nullptr) delete [] rows;
+            if (cols != nullptr) delete [] cols;
+            if (vals != nullptr) delete [] vals;
         }
     }
 };