ENH: support move sematics for get/set putback token

src/OpenFOAM/db/IOstreams/IOstreams/Istream.C

@@ -51,19 +51,27 @@ const Foam::token& Foam::Istream::peekBack() const noexcept
     return (putBackAvail_ ? putBackToken_ : token::undefinedToken);
 }
 
+// Return the putback token if available or fetch a new token
+// from the stream.
+//
+// Foam::token& Foam::Istream::peekToken()
+// {
+//     if (!putBackAvail_)
+//     {
+//         putBackToken_.reset();
+//         token tok;
+//         this->read(tok);
+//         putBackToken_ = std::move(tok);
+//     }
+//
+//     return putBackToken_;
+// }
 
-bool Foam::Istream::peekBack(token& tok)
+
+void Foam::Istream::putBackClear()
 {
-    if (putBackAvail_)
-    {
-        tok = putBackToken_;
-    }
-    else
-    {
-        tok.reset();
-    }
-
-    return putBackAvail_;
+    putBackAvail_ = false;
+    putBackToken_.reset();
 }
 
 
@@ -89,6 +97,28 @@ void Foam::Istream::putBack(const token& tok)
 }
 
 
+void Foam::Istream::putBack(token&& tok)
+{
+    if (bad())
+    {
+        FatalIOErrorInFunction(*this)
+            << "Attempt to put back onto bad stream"
+            << exit(FatalIOError);
+    }
+    else if (putBackAvail_)
+    {
+        FatalIOErrorInFunction(*this)
+            << "Attempt to put back another token"
+            << exit(FatalIOError);
+    }
+    else
+    {
+        putBackAvail_ = true;
+        putBackToken_ = std::move(tok);
+    }
+}
+
+
 bool Foam::Istream::getBack(token& tok)
 {
     if (bad())
@@ -100,7 +130,7 @@ bool Foam::Istream::getBack(token& tok)
     else if (putBackAvail_)
     {
         putBackAvail_ = false;
-        tok = putBackToken_;
+        tok = std::move(putBackToken_);
         return true;
     }
 

src/OpenFOAM/db/IOstreams/IOstreams/Istream.H

@@ -77,10 +77,7 @@ protected:
     // Protected Member Functions
 
         //- True if putback token is in use
-        bool hasPutback() const noexcept
-        {
-            return putBackAvail_;
-        }
+        bool hasPutback() const noexcept { return putBackAvail_; }
 
 
 public:
@@ -124,15 +121,16 @@ public:
             //  if a putback is unavailable.
             const token& peekBack() const noexcept;
 
-            //- Fetch putback token without removing it.
-            //  \return false sets the token to undefined if no put-back
-            //  was available
-            bool peekBack(token& tok);
+            //- Drop the putback token
+            void putBackClear();
 
-            //- Put back a token. Only a single put back is permitted
+            //- Put back a token (copy). Only a single put back is permitted
             void putBack(const token& tok);
 
-            //- Get the put-back token if there is one.
+            //- Put back a token (move). Only a single put back is permitted
+            void putBack(token&& tok);
+
+            //- Retrieve the put-back token if there is one.
             //  \return false and sets token to undefined if no put-back
             //  was available
             bool getBack(token& tok);

src/OpenFOAM/db/IOstreams/Pstreams/UIPstreamBase.C

@@ -273,6 +273,12 @@ Foam::Istream& Foam::UIPstreamBase::read(token& t)
         }
     }
 
+
+    // Reset token, adjust its line number according to the stream
+    t.reset();
+    t.lineNumber(this->lineNumber());
+
+
     // Read character, return on error
     // - with additional handling for special stream flags
 
@@ -303,9 +309,6 @@ Foam::Istream& Foam::UIPstreamBase::read(token& t)
     while (c == token::FLAG);
 
 
-    // Set the line number of this token to the current stream line number
-    t.lineNumber(this->lineNumber());
-
     // Analyse input starting with this character.
     switch (c)
     {

src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C

@@ -538,6 +538,10 @@ Foam::Istream& Foam::ISstream::read(token& t)
         return *this;
     }
 
+    // Reset token, adjust its line number according to the stream
+    t.reset();
+    t.lineNumber(this->lineNumber());
+
     // Assume that the streams supplied are in working order.
     // Lines are counted by '\n'
 
@@ -546,9 +550,6 @@ Foam::Istream& Foam::ISstream::read(token& t)
 
     char c = nextValid();
 
-    // Set the line number of this token to the current stream line number
-    t.lineNumber(this->lineNumber());
-
     // Return on error
     if (!c)
     {

src/OpenFOAM/db/IOstreams/token/token.H

@@ -510,6 +510,9 @@ public:
         //- Token is COMPOUND
         inline bool isCompound() const noexcept;
 
+        //- True if token is not UNDEFINED or ERROR. Same as good().
+        explicit operator bool() const noexcept { return good(); }
+
 
     // Access
 
@@ -690,6 +693,7 @@ public:
         void operator=(string*) = delete;
 };
 
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 // IOstream Operators