ENH: improve stream output of std::string etc.

- change write(const string&) to write(const std::string&).
  This allows output of std::string without an intermediate copy.

- additional writeQuoted method to handle range of char data:

     writeQuoted(const char* str, std::streamsize len, bool)

  This helps with supporting string_view and span<char>

- add operator<< for stdFoam::span<char> and std::string_view (c++17)

- avoid duplicate code in OBJstream

STYLE: add override keyword for IO stream methods

applications/test/compoundToken1/Test-compoundToken1.C

@@ -57,7 +57,7 @@ class IFstreamDelayed
 :
     public IFstream
 {
-    virtual bool readCompoundToken(token& tok, const word& type)
+    virtual bool readCompoundToken(token& tok, const word& type) override
     {
         auto& is = *this;
 

applications/test/string_view1/Make/files

@@ -0,0 +1,3 @@
+Test-string_view1.C
+
+EXE = $(FOAM_USER_APPBIN)/Test-string_view1

applications/test/string_view1/Make/options

@@ -0,0 +1,2 @@
+/* EXE_INC = */
+/* EXE_LIBS = */

applications/test/string_view1/Test-string_view1.C

@@ -0,0 +1,94 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Description
+    Test some string_view functionality
+
+\*---------------------------------------------------------------------------*/
+
+#include "string.H"
+#include "IOstreams.H"
+#include "List.H"
+
+using namespace Foam;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+// Main program:
+
+int main(int argc, char *argv[])
+{
+    Info<< "Compiled with C++ " << __cplusplus;
+    #if __cplusplus >= 201703L
+    Info<< " - has std::string_view" << nl << nl;
+    #else
+    Info<< " - NO std::string_view" << nl << nl;
+    #endif
+
+    // basics
+    {
+        for
+        (
+            const auto& cstr
+          :
+            {
+                "abcdef"
+            }
+        )
+        {
+            const auto len = strlen(cstr);
+
+            Info<< nl
+                << "input: <" << cstr << '>'
+                << " type: " << typeid(cstr).name() << " len:" << len << nl;
+
+            #if __cplusplus >= 201703L
+            Info<< "    view: " << std::string_view(cstr) << nl;
+            #endif
+
+            Info<< "    span: "
+                << stdFoam::span<const char>(cstr, len) << nl;
+            Info<< "    span: "
+                << stdFoam::span<char>(const_cast<char*>(cstr), len) << nl;
+        }
+    }
+
+    // This should fail to compile:
+    #if 0
+    {
+        labelList values(identity(4));
+
+        Info<< "values: " << values << nl;
+
+        Info<< "    span: "
+            << stdFoam::span<label>(values.data(), values.size()) << nl;
+    }
+    #endif
+
+    Info<< "\nEnd\n" << endl;
+    return 0;
+}
+
+
+// ************************************************************************* //

applications/utilities/finiteArea/makeFaMesh/faMeshWriteEdgesOBJ.H

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -33,11 +33,7 @@ Description
 
     OBJstream os(runTime.globalPath()/outputName);
 
-    os.writeQuoted
-    (
-        ("# " + outputName + "\n"),
-        false
-    );
+    os.writeComment(outputName);
 
     os.write(aMesh.patch().edges(), aMesh.patch().localPoints());
 }