ENH: add fileName /= operator (similar to std::filesystem::path)

src/OSspecific/POSIX/POSIX.C

@@ -824,7 +824,7 @@ bool Foam::cp(const fileName& src, const fileName& dest, const bool followLink)
         // If dest is a directory, create the destination file name.
         if (destFile.type() == fileName::DIRECTORY)
         {
-            destFile = destFile/src.name();
+            destFile /= src.name();
         }
 
         // Make sure the destination directory exists.
@@ -864,7 +864,7 @@ bool Foam::cp(const fileName& src, const fileName& dest, const bool followLink)
         // If dest is a directory, create the destination file name.
         if (destFile.type() == fileName::DIRECTORY)
         {
-            destFile = destFile/src.name();
+            destFile /= src.name();
         }
 
         // Make sure the destination directory exists.
@@ -880,7 +880,7 @@ bool Foam::cp(const fileName& src, const fileName& dest, const bool followLink)
         // If dest is a directory, create the destination file name.
         if (destFile.type() == fileName::DIRECTORY)
         {
-            destFile = destFile/src.components().last();
+            destFile /= src.components().last();
         }
 
         // Make sure the destination directory exists.

src/OpenFOAM/primitives/strings/fileName/fileName.C

@@ -533,6 +533,30 @@ void Foam::fileName::operator=(const char* str)
 }
 
 
+Foam::fileName& Foam::fileName::operator/=(const string& other)
+{
+    fileName& s = *this;
+
+    if (s.size())
+    {
+        if (other.size())
+        {
+            // Two non-empty strings: can concatenate
+
+            s.append("/");
+            s.append(other);
+        }
+    }
+    else if (other.size())
+    {
+        // Or, if the first string is empty
+        s = other;
+    }
+
+    return *this;
+}
+
+
 // * * * * * * * * * * * * * * * Global Operators  * * * * * * * * * * * * * //
 
 Foam::fileName Foam::operator/(const string& a, const string& b)

src/OpenFOAM/primitives/strings/fileName/fileName.H

@@ -130,7 +130,7 @@ public:
         fileName(Istream& is);
 
 
-    // Member functions
+    // Member Functions
 
         //- Is this character valid for a fileName?
         inline static bool valid(char c);
@@ -334,6 +334,13 @@ public:
         void operator=(const char* str);
 
 
+    // Other operators
+
+        //- Append a path element with '/' separator.
+        //  No '/' separator is added if this or the argument are empty.
+        fileName& operator/=(const string& other);
+
+
     // IOstream operators
 
         friend Istream& operator>>(Istream& is, fileName& fn);