ENH: lazy evaluation of subRegion in regionFunctionObject (#1202)

- delay dereferencing of optional subRegion entries until an
  objectRegistry is required.

  This improves usabilty when reference objects do not yet exist
  at the time of construction.

src/OpenFOAM/db/functionObjects/regionFunctionObject/regionFunctionObject.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2016 OpenCFD Ltd.
+    \\  /    A nd           | Copyright (C) 2016-2019 OpenCFD Ltd.
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
                             | Copyright (C) 2016 OpenFOAM Foundation
@@ -42,27 +42,23 @@ namespace functionObjects
 
 // * * * * * * * * * * * * * Protected Member Functions  * * * * * * * * * * //
 
-const Foam::objectRegistry&
-Foam::functionObjects::regionFunctionObject::whichSubRegistry
-(
-    const objectRegistry& obr,
-    const dictionary& dict
-)
-{
-    word subName;
-    if (dict.readIfPresent("subRegion", subName))
-    {
-        return obr.lookupObject<objectRegistry>(subName);
-    }
-
-    return obr;
-}
-
-
 const Foam::objectRegistry&
 Foam::functionObjects::regionFunctionObject::obr() const
 {
-    return subObr_;
+    if (!obrPtr_ && !subRegistryName_.empty())
+    {
+        // Recursive - so we also find things registered on Time
+        obrPtr_ = obr_.cfindObject<objectRegistry>(subRegistryName_, true);
+
+        // Also search functionObject output ("functionObjectObjects")
+        if (!obrPtr_)
+        {
+            obrPtr_ =
+                storedObjects().cfindObject<objectRegistry>(subRegistryName_);
+        }
+    }
+
+    return (obrPtr_ ? *obrPtr_ : obr_);
 }
 
 
@@ -140,6 +136,7 @@ Foam::functionObjects::regionFunctionObject::regionFunctionObject
 )
 :
     stateFunctionObject(name, runTime),
+    subRegistryName_(dict.lookupOrDefault<word>("subRegion", word::null)),
     obr_
     (
         runTime.lookupObject<objectRegistry>
@@ -147,7 +144,7 @@ Foam::functionObjects::regionFunctionObject::regionFunctionObject
             dict.lookupOrDefault("region", polyMesh::defaultRegion)
         )
     ),
-    subObr_(whichSubRegistry(obr_, dict))
+    obrPtr_(nullptr)
 {}
 
 
@@ -159,8 +156,9 @@ Foam::functionObjects::regionFunctionObject::regionFunctionObject
 )
 :
     stateFunctionObject(name, obr.time()),
+    subRegistryName_(dict.lookupOrDefault<word>("subRegion", word::null)),
     obr_(obr),
-    subObr_(whichSubRegistry(obr_, dict))
+    obrPtr_(nullptr)
 {}
 
 
@@ -168,7 +166,13 @@ Foam::functionObjects::regionFunctionObject::regionFunctionObject
 
 bool Foam::functionObjects::regionFunctionObject::read(const dictionary& dict)
 {
-    return stateFunctionObject::read(dict);
+    stateFunctionObject::read(dict);
+
+    subRegistryName_ = dict.lookupOrDefault<word>("subRegion", word::null);
+
+    obrPtr_ = nullptr;
+
+    return true;
 }
 
 

src/OpenFOAM/db/functionObjects/regionFunctionObject/regionFunctionObject.H

@@ -29,8 +29,17 @@ Class
 Description
     Specialization of Foam::functionObject for a region and providing a
     reference to the region Foam::objectRegistry.
-    Also provides support for referencing a sub-region, which is typically
-    needed when dealing with surfMesh and their fields.
+
+    Also provides support for referencing an alternative objectRegistry
+    that can hold fields. This may be used, for example, to access
+    stored surfaces and fields.
+
+    Dictionary controls
+    \table
+        Property    | Description                           | Required | Default
+        region      | Name of the mesh region               | no | region0
+        subRegion   | Name for alternative objectRegistry   | no | ""
+    \endtable
 
 See also
     Foam::functionObjects::stateFunctionObject
@@ -69,25 +78,19 @@ protected:
 
     // Protected Member Data
 
+        //- Name for alternative object registry
+        word subRegistryName_;
+
         //- Reference to the region objectRegistry
         const objectRegistry& obr_;
 
-        //- Optional reference to the sub-region objectRegistry.
-        //  If a sub-region is not in effect, this reference is identical
-        //  to the usual region objectRegistry.
-        const objectRegistry& subObr_;
+        //- Pointer to alternative (eg, sub-region) objectRegistry.
+        //  If a sub-region is not in effect, this is a nullptr
+        mutable const objectRegistry* obrPtr_;
 
 
     // Protected Member Functions
 
-        //- Selector for alternative sub-registry,
-        //  when the keyword %subRegion is present in the dictionary
-        static const objectRegistry& whichSubRegistry
-        (
-            const objectRegistry& obr,
-            const dictionary& dict
-        );
-
         //- The region or sub-region registry being used
         virtual const objectRegistry& obr() const;