diff --git a/src/OpenFOAM/containers/Lists/DynamicList/DynamicList.H b/src/OpenFOAM/containers/Lists/DynamicList/DynamicList.H
index c074820f4c..46fae4d5e7 100644
--- a/src/OpenFOAM/containers/Lists/DynamicList/DynamicList.H
+++ b/src/OpenFOAM/containers/Lists/DynamicList/DynamicList.H
@@ -250,7 +250,7 @@ public:
 
         //- Swap content, independent of sizing parameter
         template<int AnySizeMin>
-        inline void swap(DynamicList<T, AnySizeMin>& other);
+        inline void swap(DynamicList<T, AnySizeMin>& other) noexcept;
 
         //- Transfer contents of the argument List into this.
         inline void transfer(List<T>& list);
diff --git a/src/OpenFOAM/containers/Lists/DynamicList/DynamicListI.H b/src/OpenFOAM/containers/Lists/DynamicList/DynamicListI.H
index 27d3209987..ccf07d15a5 100644
--- a/src/OpenFOAM/containers/Lists/DynamicList/DynamicListI.H
+++ b/src/OpenFOAM/containers/Lists/DynamicList/DynamicListI.H
@@ -373,6 +373,18 @@ inline void Foam::DynamicList<T, SizeMin>::resize_nocopy
 }
 
 
+// template<class T, int SizeMin>
+// inline void Foam::DynamicList<T, SizeMin>::resize_fill
+// (
+//     const label len,
+//     const T& val
+// )
+// {
+//     this->doResize(true, len);  // nocopy = true
+//     this->fill_uniform(val);
+// }
+
+
 template<class T, int SizeMin>
 inline void Foam::DynamicList<T, SizeMin>::resize
 (
@@ -448,7 +460,7 @@ template<int AnySizeMin>
 inline void Foam::DynamicList<T, SizeMin>::swap
 (
     DynamicList<T, AnySizeMin>& other
-)
+) noexcept
 {
     if
     (
diff --git a/src/OpenFOAM/containers/Lists/DynamicList/DynamicListIO.C b/src/OpenFOAM/containers/Lists/DynamicList/DynamicListIO.C
index 5fa5e9d00f..37b7ae822d 100644
--- a/src/OpenFOAM/containers/Lists/DynamicList/DynamicListIO.C
+++ b/src/OpenFOAM/containers/Lists/DynamicList/DynamicListIO.C
@@ -43,13 +43,10 @@ Foam::DynamicList<T, SizeMin>::DynamicList(Istream& is)
 }
 
 
-// * * * * * * * * * * * * * * * IOstream Operators  * * * * * * * * * * * * //
+// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
 
 template<class T, int SizeMin>
-Foam::Istream& Foam::DynamicList<T, SizeMin>::readList
-(
-    Istream& is
-)
+Foam::Istream& Foam::DynamicList<T, SizeMin>::readList(Istream& is)
 {
     DynamicList<T, SizeMin>& list = *this;
 
diff --git a/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H b/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
index 25874664b5..68144b2df5 100644
--- a/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
+++ b/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
@@ -28,6 +28,7 @@ License
 
 #include "UList.H"
 #include "SLList.H"
+// <algorithm> already included by stdFoam.H
 
 // * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
 
@@ -372,6 +373,7 @@ inline void Foam::FixedList<T, N>::resize_nocopy(const label n)
 template<class T, unsigned N>
 inline void Foam::FixedList<T, N>::fill(const T& val)
 {
+    // Usually small enough that parallel execution is pointless...
     for (unsigned i=0; i<N; ++i)
     {
         v_[i] = val;
@@ -382,6 +384,7 @@ inline void Foam::FixedList<T, N>::fill(const T& val)
 template<class T, unsigned N>
 inline void Foam::FixedList<T, N>::fill(const Foam::zero)
 {
+    // Usually small enough that parallel execution is pointless...
     for (unsigned i=0; i<N; ++i)
     {
         v_[i] = Zero;
diff --git a/src/OpenFOAM/containers/Lists/FixedList/FixedListIO.C b/src/OpenFOAM/containers/Lists/FixedList/FixedListIO.C
index 62baf65e13..c4e7a5157f 100644
--- a/src/OpenFOAM/containers/Lists/FixedList/FixedListIO.C
+++ b/src/OpenFOAM/containers/Lists/FixedList/FixedListIO.C
@@ -244,10 +244,8 @@ Foam::Istream& Foam::FixedList<T, N>::readList
                 "reading the single entry"
             );
 
-            for (unsigned i=0; i<N; ++i)
-            {
-                list[i] = elem;  // Copy the value
-            }
+            // Fill with the value
+            this->fill(elem);
         }
 
         // End of contents marker
diff --git a/src/OpenFOAM/containers/Lists/List/List.C b/src/OpenFOAM/containers/Lists/List/List.C
index 55ea1f56a5..1b728d37c0 100644
--- a/src/OpenFOAM/containers/Lists/List/List.C
+++ b/src/OpenFOAM/containers/Lists/List/List.C
@@ -54,7 +54,7 @@ void Foam::List<T>::doResize(const label len)
             // - when used as storage for DynamicList, it is possible to have
             //   a zero-sized List with a non-null data pointer.
 
-            if (this->v_) delete[] this->v_;
+            delete[] this->v_;
             this->size_ = len;
             this->v_ = new T[len];
         }
@@ -64,7 +64,9 @@ void Foam::List<T>::doResize(const label len)
 
             T* nv = new T[len];
 
-            // ie, std::copy(this->v_, this->v_ + overlap, nv);
+            // Like std::copy(this->v_, this->v_ + overlap, nv);
+            // but with move semantics!
+
             #ifdef USEMEMCPY
             if (is_contiguous<T>::value)
             {
@@ -137,12 +139,7 @@ Foam::List<T>::List(const label len, const T& val)
     if (len)
     {
         doAlloc();
-
-        List_ACCESS(T, (*this), vp);
-        for (label i=0; i < len; ++i)
-        {
-            vp[i] = val;
-        }
+        this->fill_uniform(val);
     }
 }
 
@@ -163,8 +160,9 @@ Foam::List<T>::List(const label len, const Foam::zero)
     {
         doAlloc();
 
+        // fill_uniform()
         List_ACCESS(T, (*this), vp);
-        for (label i=0; i < len; ++i)
+        for (label i = 0; i < len; ++i)
         {
             vp[i] = Zero;
         }
@@ -200,109 +198,49 @@ Foam::List<T>::List(const Foam::one, const Foam::zero)
 
 
 template<class T>
-Foam::List<T>::List(const UList<T>& a)
+Foam::List<T>::List(const UList<T>& list)
 :
-    UList<T>(nullptr, a.size_)
+    UList<T>(nullptr, list.size_)
 {
-    const label len = this->size_;
-
-    if (len)
+    if (this->size_ > 0)
     {
         doAlloc();
-
-        #ifdef USEMEMCPY
-        if (is_contiguous<T>::value)
-        {
-            std::memcpy
-            (
-                static_cast<void*>(this->v_), a.v_, this->size_bytes()
-            );
-        }
-        else
-        #endif
-        {
-            List_ACCESS(T, (*this), vp);
-            List_CONST_ACCESS(T, a, ap);
-            for (label i = 0; i < len; ++i)
-            {
-                vp[i] = ap[i];
-            }
-        }
+        UList<T>::deepCopy(list);
     }
 }
 
 
 template<class T>
-Foam::List<T>::List(const List<T>& a)
+Foam::List<T>::List(const List<T>& list)
 :
-    UList<T>(nullptr, a.size_)
+    UList<T>(nullptr, list.size_)
 {
-    const label len = this->size_;
-
-    if (len)
+    if (this->size_ > 0)
     {
         doAlloc();
-
-        #ifdef USEMEMCPY
-        if (is_contiguous<T>::value)
-        {
-            std::memcpy
-            (
-                static_cast<void*>(this->v_), a.v_, this->size_bytes()
-            );
-        }
-        else
-        #endif
-        {
-            List_ACCESS(T, (*this), vp);
-            List_CONST_ACCESS(T, a, ap);
-            for (label i = 0; i < len; ++i)
-            {
-                vp[i] = ap[i];
-            }
-        }
+        UList<T>::deepCopy(list);
     }
 }
 
 
 template<class T>
-Foam::List<T>::List(List<T>& a, bool reuse)
+Foam::List<T>::List(List<T>& list, bool reuse)
 :
-    UList<T>(nullptr, a.size_)
+    UList<T>(nullptr, list.size_)
 {
     if (reuse)
     {
         // Steal content
-        this->v_ = a.v_;
-        a.v_ = nullptr;
-        a.size_ = 0;
+        this->v_ = list.v_;
+        list.v_ = nullptr;
+        list.size_ = 0;
         return;
     }
 
-    const label len = this->size_;
-
-    if (len)
+    if (this->size_)
     {
         doAlloc();
-
-        #ifdef USEMEMCPY
-        if (is_contiguous<T>::value)
-        {
-            std::memcpy
-            (
-                static_cast<void*>(this->v_), a.v_, this->size_bytes()
-            );
-        }
-        else
-        #endif
-        {
-            List_ACCESS(T, (*this), vp);
-            List_CONST_ACCESS(T, a, ap);
-            for (label i = 0; i < len; ++i)
-            {
-                vp[i] = ap[i];
-            }
-        }
+        UList<T>::deepCopy(list);
     }
 }
 
@@ -318,6 +256,7 @@ Foam::List<T>::List(const UList<T>& list, const labelUList& indices)
     {
         doAlloc();
 
+        // Copy indirect
         List_ACCESS(T, (*this), vp);
 
         for (label i=0; i < len; ++i)
@@ -340,13 +279,16 @@ Foam::List<T>::List
 {
     const label len = label(N);
 
-    doAlloc();
-
-    List_ACCESS(T, (*this), vp);
-
-    for (label i=0; i < len; ++i)
     {
-        vp[i] = list[indices[i]];
+        doAlloc();
+
+        // Copy indirect
+        List_ACCESS(T, (*this), vp);
+
+        for (label i = 0; i < len; ++i)
+        {
+            vp[i] = list[indices[i]];
+        }
     }
 }
 
@@ -431,10 +373,7 @@ Foam::List<T>::List(SLList<T>&& list)
 template<class T>
 Foam::List<T>::~List()
 {
-    if (this->v_)
-    {
-        delete[] this->v_;
-    }
+    delete[] this->v_;
 }
 
 
@@ -443,14 +382,16 @@ Foam::List<T>::~List()
 template<class T>
 void Foam::List<T>::resize(const label len, const T& val)
 {
-    label idx = this->size_;
+    const label oldLen = this->size_;
     this->doResize(len);
 
-    List_ACCESS(T, *this, vp);
-    while (idx < len)
+    // Fill trailing part with new values
+    if (oldLen < this->size_)
     {
-        vp[idx] = val;
-        ++idx;
+        std::fill
+        (
+            (this->v_ + oldLen), (this->v_ + this->size_), val
+        );
     }
 }
 
@@ -463,7 +404,7 @@ void Foam::List<T>::transfer(List<T>& list)
         return;  // Self-assignment is a no-op
     }
 
-    // Clear and swap - could also check for self assignment
+    // Clear and swap
     clear();
     this->size_ = list.size_;
     this->v_ = list.v_;
@@ -489,37 +430,18 @@ void Foam::List<T>::transfer(DynamicList<T, SizeMin>& list)
 // * * * * * * * * * * * * * * * Member Operators  * * * * * * * * * * * * * //
 
 template<class T>
-void Foam::List<T>::operator=(const UList<T>& a)
+void Foam::List<T>::operator=(const UList<T>& list)
 {
-    if (this == &a)
+    if (this == &list)
     {
         return;  // Self-assignment is a no-op
     }
 
-    reAlloc(a.size_);
+    reAlloc(list.size_);
 
-    const label len = this->size_;
-
-    if (len)
+    if (this->size_ > 0)
     {
-        #ifdef USEMEMCPY
-        if (is_contiguous<T>::value)
-        {
-            std::memcpy
-            (
-                static_cast<void*>(this->v_), a.v_, this->size_bytes()
-            );
-        }
-        else
-        #endif
-        {
-            List_ACCESS(T, (*this), vp);
-            List_CONST_ACCESS(T, a, ap);
-            for (label i = 0; i < len; ++i)
-            {
-                vp[i] = ap[i];
-            }
-        }
+        UList<T>::deepCopy(list);
     }
 }
 
@@ -532,7 +454,12 @@ void Foam::List<T>::operator=(const List<T>& list)
         return;  // Self-assignment is a no-op
     }
 
-    operator=(static_cast<const UList<T>&>(list));
+    reAlloc(list.size_);
+
+    if (this->size_ > 0)
+    {
+        UList<T>::deepCopy(list);
+    }
 }
 
 
@@ -545,6 +472,8 @@ void Foam::List<T>::operator=(const SLList<T>& list)
 
     if (len)
     {
+        // std::copy(list.begin(), list.end(), this->v_);
+
         T* iter = this->begin();
 
         for (const T& val : list)
@@ -582,6 +511,7 @@ void Foam::List<T>::operator=(const IndirectListBase<T, Addr>& list)
 
     if (len)
     {
+        // copyList ...
         List_ACCESS(T, (*this), vp);
 
         for (label i=0; i < len; ++i)
diff --git a/src/OpenFOAM/containers/Lists/List/List.H b/src/OpenFOAM/containers/Lists/List/List.H
index 0a6cce2a94..b1a398eb67 100644
--- a/src/OpenFOAM/containers/Lists/List/List.H
+++ b/src/OpenFOAM/containers/Lists/List/List.H
@@ -85,7 +85,7 @@ class List
         //  Discards old storage (if any). Does not copy old contents
         inline void reAlloc(const label len);
 
-        //- Copy all list contents
+        //- Copy all list contents. Uses operator[] on the input list
         template<class List2>
         inline void copyList(const List2& list);
 
@@ -142,13 +142,13 @@ public:
         List(const Foam::one, const Foam::zero);
 
         //- Copy construct from list
-        List(const List<T>& a);
+        List(const List<T>& list);
 
         //- Copy construct contents from list
-        explicit List(const UList<T>& a);
+        explicit List(const UList<T>& list);
 
         //- Construct as copy or re-use as specified
-        List(List<T>& a, bool reuse);
+        List(List<T>& list, bool reuse);
 
         //- Copy construct subset of list
         List(const UList<T>& list, const labelUList& indices);
diff --git a/src/OpenFOAM/containers/Lists/List/ListI.H b/src/OpenFOAM/containers/Lists/List/ListI.H
index 0ae68fbf20..6c8aec1f3e 100644
--- a/src/OpenFOAM/containers/Lists/List/ListI.H
+++ b/src/OpenFOAM/containers/Lists/List/ListI.H
@@ -55,11 +55,14 @@ template<class T>
 template<class List2>
 inline void Foam::List<T>::copyList(const List2& list)
 {
+    // NB: operator[] for list read access (eg, an indirect list)
+    // cannot necessarily replace with std::copy
+
     const label len = this->size_;
 
-    for (label i=0; i<len; ++i)
+    for (label i = 0; i < len; ++i)
     {
-        this->operator[](i) = list[i];
+        this->v_[i] = list[i];
     }
 }
 
@@ -79,10 +82,13 @@ inline Foam::List<T>::List
     {
         doAlloc();
 
+        // Like std::copy() or std::copy_n()
+        // but without any requirements on the iterator category
+
         InputIterator iter = begIter;
         for (label i = 0; i < len; ++i)
         {
-            this->operator[](i) = *iter;
+            this->v_[i] = *iter;
             ++iter;
         }
     }
@@ -149,6 +155,14 @@ inline void Foam::List<T>::resize_nocopy(const label len)
 }
 
 
+// template<class T>
+// inline void Foam::List<T>::resize_fill(const label len, const T& val)
+// {
+//     this->reAlloc(len);
+//     this->fill_uniform(val);
+// }
+
+
 template<class T>
 inline T& Foam::List<T>::newElmt(const label i)
 {
diff --git a/src/OpenFOAM/containers/Lists/List/ListIO.C b/src/OpenFOAM/containers/Lists/List/ListIO.C
index 3db5928d19..8faf41238f 100644
--- a/src/OpenFOAM/containers/Lists/List/ListIO.C
+++ b/src/OpenFOAM/containers/Lists/List/ListIO.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2018-2022 OpenCFD Ltd.
+    Copyright (C) 2018-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -50,9 +50,6 @@ Foam::Istream& Foam::List<T>::readList(Istream& is)
 {
     List<T>& list = *this;
 
-    // Anull list
-    list.clear();
-
     is.fatalCheck(FUNCTION_NAME);
 
     token tok(is);
@@ -63,6 +60,7 @@ Foam::Istream& Foam::List<T>::readList(Istream& is)
     {
         // Compound: simply transfer contents
 
+        list.clear();  // Clear old contents
         list.transfer
         (
             dynamicCast<token::Compound<List<T>>>
@@ -77,8 +75,8 @@ Foam::Istream& Foam::List<T>::readList(Istream& is)
 
         const label len = tok.labelToken();
 
-        // Resize to actual length read
-        list.resize(len);
+        // Resize to length required
+        list.resize_nocopy(len);
 
         if (is.format() == IOstreamOption::BINARY && is_contiguous<T>::value)
         {
@@ -96,7 +94,7 @@ Foam::Istream& Foam::List<T>::readList(Istream& is)
                 is.fatalCheck
                 (
                     "List<T>::readList(Istream&) : "
-                    "reading the binary block"
+                    "reading binary block"
                 );
             }
         }
@@ -133,10 +131,8 @@ Foam::Istream& Foam::List<T>::readList(Istream& is)
                         "reading the single entry"
                     );
 
-                    for (label i=0; i<len; ++i)
-                    {
-                        list[i] = elem;  // Copy the value
-                    }
+                    // Fill with the value
+                    this->fill_uniform(elem);
                 }
             }
 
@@ -148,6 +144,8 @@ Foam::Istream& Foam::List<T>::readList(Istream& is)
     {
         // "(...)" : read as SLList and transfer contents
 
+        list.clear();  // Clear old contents
+
         is.putBack(tok);    // Putback the opening bracket
         SLList<T> sll(is);  // Read as singly-linked list
 
@@ -156,6 +154,8 @@ Foam::Istream& Foam::List<T>::readList(Istream& is)
     }
     else
     {
+        list.clear();  // Clear old contents
+
         FatalIOErrorInFunction(is)
             << "incorrect first token, expected <int> or '(', found "
             << tok.info() << nl
diff --git a/src/OpenFOAM/containers/Lists/List/UList.C b/src/OpenFOAM/containers/Lists/List/UList.C
index 4a16d82fd3..41ef2c32d5 100644
--- a/src/OpenFOAM/containers/Lists/List/UList.C
+++ b/src/OpenFOAM/containers/Lists/List/UList.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2022 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -105,35 +105,20 @@ void Foam::UList<T>::swapLast(const label i)
 template<class T>
 void Foam::UList<T>::deepCopy(const UList<T>& list)
 {
-    const label len = this->size_;
-
-    if (len != list.size_)
+    if (this->size_ != list.size_)
     {
         FatalErrorInFunction
             << "Lists have different sizes: "
-            << len << " != " << list.size() << nl
+            << this->size_ << " != " << list.size() << nl
             << abort(FatalError);
     }
-    else if (len)
+    else if (this->size_ > 0)
     {
-        #ifdef USEMEMCPY
-        if (is_contiguous<T>::value)
-        {
-            std::memcpy
-            (
-                static_cast<void*>(this->v_), list.v_, this->size_bytes()
-            );
-        }
-        else
-        #endif
-        {
-            List_ACCESS(T, (*this), lhs);
-            List_CONST_ACCESS(T, list, rhs);
-            for (label i = 0; i < len; ++i)
-            {
-                lhs[i] = rhs[i];
-            }
-        }
+        // Can also dispatch with
+        // - std::execution::parallel_unsequenced_policy
+        // - std::execution::unsequenced_policy
+
+        std::copy(list.cbegin(), list.cend(), this->v_);
     }
 }
 
@@ -142,17 +127,19 @@ template<class T>
 template<class Addr>
 void Foam::UList<T>::deepCopy(const IndirectListBase<T, Addr>& list)
 {
-    const label len = this->size_;
-
-    if (len != list.size())
+    if (this->size_ != list.size())
     {
         FatalErrorInFunction
             << "Lists have different sizes: "
-            << len << " != " << list.size() << nl
+            << this->size_ << " != " << list.size() << nl
             << abort(FatalError);
     }
-    else if (len)
+    else if (this->size_)
     {
+        // copyList()
+
+        const label len = this->size_;
+
         List_ACCESS(T, (*this), lhs);
         for (label i = 0; i < len; ++i)
         {
@@ -164,28 +151,15 @@ void Foam::UList<T>::deepCopy(const IndirectListBase<T, Addr>& list)
 
 // * * * * * * * * * * * * * * * Member Operators  * * * * * * * * * * * * * //
 
-template<class T>
-void Foam::UList<T>::operator=(const T& val)
-{
-    const label len = this->size();
-
-    List_ACCESS(T, (*this), vp);
-
-    for (label i=0; i < len; ++i)
-    {
-        vp[i] = val;
-    }
-}
-
-
 template<class T>
 void Foam::UList<T>::operator=(const Foam::zero)
 {
+    // fill_uniform()
     const label len = this->size();
 
     List_ACCESS(T, (*this), vp);
 
-    for (label i=0; i < len; ++i)
+    for (label i = 0; i < len; ++i)
     {
         vp[i] = Zero;
     }
diff --git a/src/OpenFOAM/containers/Lists/List/UList.H b/src/OpenFOAM/containers/Lists/List/UList.H
index 01d5d1b562..45caa1bc0c 100644
--- a/src/OpenFOAM/containers/Lists/List/UList.H
+++ b/src/OpenFOAM/containers/Lists/List/UList.H
@@ -118,6 +118,10 @@ protected:
         //- always addresses a valid section of the list.
         labelRange validateRange(const labelRange& requestedRange) const;
 
+        //- Assign all entries to the given value
+        //  Caution: method name subject to change
+        inline void fill_uniform(const T& val);
+
         //- No copy assignment (default: shallow copy)
         //
         //  Assignment may need to be shallow (copy pointer)
@@ -347,7 +351,7 @@ public:
     // Copy
 
         //- Copy the pointer and size held by the given UList
-        inline void shallowCopy(const UList<T>& list);
+        inline void shallowCopy(const UList<T>& list) noexcept;
 
         //- Copy elements of the given UList. Sizes must match!
         void deepCopy(const UList<T>& list);
@@ -390,7 +394,7 @@ public:
         inline operator const Foam::List<T>&() const;
 
         //- Assignment of all entries to the given value
-        void operator=(const T& val);
+        inline void operator=(const T& val);
 
         //- Assignment of all entries to zero
         void operator=(const Foam::zero);
@@ -468,7 +472,7 @@ public:
         static constexpr label max_size() noexcept { return labelMax; }
 
         //- Swap content with another UList of the same type in constant time
-        inline void swap(UList<T>& list);
+        inline void swap(UList<T>& list) noexcept;
 
 
     // STL member operators
@@ -703,15 +707,12 @@ template<class T>
 struct Hash<UList<T>> : UList<T>::hasher {};
 
 
-//- Object access operator or list access operator.
+//- Object access operator or list access operator (default is pass-through)
 //- \sa ListListOps::combine()
 template<class T>
 struct accessOp
 {
-    const T& operator()(const T& obj) const
-    {
-        return obj;  // Default is pass-through
-    }
+    const T& operator()(const T& obj) const { return obj; }
 };
 
 
@@ -719,10 +720,7 @@ struct accessOp
 template<class T>
 struct emptyOp
 {
-    bool operator()(const T& obj) const
-    {
-        return obj.empty();
-    }
+    bool operator()(const T& obj) const { return obj.empty(); }
 };
 
 
@@ -730,10 +728,7 @@ struct emptyOp
 template<class T>
 struct sizeOp
 {
-    label operator()(const T& obj) const
-    {
-        return obj.size();
-    }
+    label operator()(const T& obj) const { return obj.size(); }
 };
 
 
diff --git a/src/OpenFOAM/containers/Lists/List/UListI.H b/src/OpenFOAM/containers/Lists/List/UListI.H
index 183b5e6893..a56999a068 100644
--- a/src/OpenFOAM/containers/Lists/List/UListI.H
+++ b/src/OpenFOAM/containers/Lists/List/UListI.H
@@ -27,6 +27,7 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "error.H"
+// <algorithm> already included by stdFoam.H
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
@@ -46,6 +47,25 @@ inline Foam::UList<T>::UList(T* __restrict__ v, const label len) noexcept
 {}
 
 
+// * * * * * * * * * * * * Protected Member Functions  * * * * * * * * * * * //
+
+template<class T>
+inline void Foam::UList<T>::fill_uniform(const T& val)
+{
+    // Can also dispatch with
+    // - std::execution::parallel_unsequenced_policy
+    // - std::execution::unsequenced_policy
+
+    if (this->size_ > 0)
+    {
+        std::fill_n
+        (
+            this->v_, this->size_, val
+        );
+    }
+}
+
+
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 template<class T>
@@ -268,7 +288,7 @@ inline bool Foam::UList<T>::contains(const T& val, label pos) const
 
 
 template<class T>
-inline void Foam::UList<T>::shallowCopy(const UList<T>& list)
+inline void Foam::UList<T>::shallowCopy(const UList<T>& list) noexcept
 {
     size_ = list.size_;
     v_ = list.v_;
@@ -277,6 +297,13 @@ inline void Foam::UList<T>::shallowCopy(const UList<T>& list)
 
 // * * * * * * * * * * * * * * * Member Operators  * * * * * * * * * * * * * //
 
+template<class T>
+inline void Foam::UList<T>::operator=(const T& val)
+{
+    this->fill_uniform(val);
+}
+
+
 namespace Foam
 {
     // Template specialization for bool
@@ -439,7 +466,7 @@ inline void Foam::UList<T>::setAddressableSize(const label n) noexcept
 
 
 template<class T>
-inline void Foam::UList<T>::swap(UList<T>& list)
+inline void Foam::UList<T>::swap(UList<T>& list) noexcept
 {
     if (&list == this)
     {
diff --git a/src/OpenFOAM/containers/Lists/List/UListIO.C b/src/OpenFOAM/containers/Lists/List/UListIO.C
index 80285f51a9..36ccdd4a4f 100644
--- a/src/OpenFOAM/containers/Lists/List/UListIO.C
+++ b/src/OpenFOAM/containers/Lists/List/UListIO.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2016-2022 OpenCFD Ltd.
+    Copyright (C) 2016-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -264,10 +264,8 @@ Foam::Istream& Foam::UList<T>::readList(Istream& is)
                         "reading the single entry"
                     );
 
-                    for (label i=0; i<len; ++i)
-                    {
-                        list[i] = elem;  // Copy the value
-                    }
+                    // Fill with the value
+                    this->fill_uniform(elem);
                 }
             }