ENH: add UPtrList method to squeeze out (remove) null pointers

- moves any nullptr to the end of the list where they can be
  eliminated in a second step with resize()

applications/test/PtrList/Test-PtrList.C

@@ -488,6 +488,33 @@ int main(int argc, char *argv[])
 
     report(Info, dynPlanes, true);
 
+    {
+        // No clone for plane - do manual copy
+        PtrList<plane> stdPlanes(dynPlanes.size());
+
+        forAll(dynPlanes, i)
+        {
+            const plane* pln = dynPlanes.set(i);
+            if (pln)
+            {
+                stdPlanes.set(i, new plane(*pln));
+            }
+        }
+
+        report(Info, stdPlanes);
+        printAddr(Info, stdPlanes);
+
+        stdPlanes.resize(stdPlanes.squeezeNull());
+
+        Info<<"After pruning nullptr entries" << endl;
+        printAddr(Info, stdPlanes);
+    }
+
+    dynPlanes.resize(dynPlanes.squeezeNull());
+
+    Info<<"After pruning nullptr entries" << endl;
+    report(Info, dynPlanes, true);
+
     Info<<"free()" << endl;
 
     dynPlanes.free();

src/OpenFOAM/containers/PtrLists/PtrDynList/PtrDynList.H

@@ -106,7 +106,7 @@ public:
         //- Alter the addressed list size.
         inline void resize(const label newLen);
 
-        //- Alter the addressed list size.
+        //- Same as resize()
         inline void setSize(const label newLen);
 
         //- Reserve allocation space for at least this size.
@@ -139,8 +139,9 @@ public:
         //- Remove and return the top element
         inline autoPtr<T> remove();
 
-        //- Return true if element is set (ie, not a nullptr)
-        inline bool set(const label i) const;
+        //- Return const pointer to element (if set) or nullptr.
+        //  The return value can be tested as a bool.
+        inline const T* set(const label i) const;
 
         //- Set element to given pointer and return old element (can be null)
         inline autoPtr<T> set(const label i, T* ptr);

src/OpenFOAM/containers/PtrLists/PtrDynList/PtrDynListI.H

@@ -243,9 +243,9 @@ inline Foam::autoPtr<T> Foam::PtrDynList<T, SizeMin>::remove()
 
 
 template<class T, int SizeMin>
-inline bool Foam::PtrDynList<T, SizeMin>::set(const label i) const
+inline const T* Foam::PtrDynList<T, SizeMin>::set(const label i) const
 {
-    return (i >= 0 && i < PtrList<T>::size()) ? PtrList<T>::set(i) : false;
+    return (i >= 0 && i < PtrList<T>::size()) ? PtrList<T>::set(i) : nullptr;
 }
 
 

src/OpenFOAM/containers/PtrLists/PtrList/PtrList.H

@@ -131,8 +131,7 @@ public:
         //  New entries are initialized to nullptr, removed entries are deleted
         void resize(const label newLen);
 
-        //- Adjust size of PtrList.
-        //  New entries are initialized to nullptr, removed entries are deleted
+        //- Same as resize()
         inline void setSize(const label newLen);
 
         //- Append an element to the end of the list

src/OpenFOAM/containers/PtrLists/UPtrList/UPtrList.C

@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
-     \\/     M anipulation  | Copyright (C) 2015-2018 OpenCFD Ltd.
+     \\/     M anipulation  | Copyright (C) 2015-2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -38,6 +38,30 @@ Foam::UPtrList<T>::UPtrList(PtrList<T>& list)
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
+template<class T>
+Foam::label Foam::UPtrList<T>::squeezeNull()
+{
+    const label len = this->size();
+    label newLen = 0;
+
+    for (label i=0; i < len; ++i)
+    {
+        T* ptr = ptrs_[i];
+        if (ptr)
+        {
+            if (i != newLen)
+            {
+                ptrs_[newLen] = ptr;
+                ptrs_[i] = nullptr;
+            }
+            ++newLen;
+        }
+    }
+
+    return newLen;
+}
+
+
 template<class T>
 void Foam::UPtrList<T>::reorder(const labelUList& oldToNew)
 {

src/OpenFOAM/containers/PtrLists/UPtrList/UPtrList.H

@@ -132,7 +132,7 @@ public:
         inline explicit UPtrList(UList<T>& list);
 
 
-    // Member functions
+    // Member Functions
 
     // Access
 
@@ -164,10 +164,13 @@ public:
         //  New entries are initialized to nullptr.
         inline void resize(const label newLen);
 
-        //- Reset size of list.
-        //  New entries are initialized to nullptr.
+        //- Same as resize()
         inline void setSize(const label newLen);
 
+        //- Squeeze out intermediate nullptr entries in the list of pointers
+        //  \return the number of non-null entries
+        label squeezeNull();
+
         //- Append an element to the end of the list
         inline void append(T* ptr);