diff --git a/src/Benchmarks/BLAS/tnl-benchmark-blas.h b/src/Benchmarks/BLAS/tnl-benchmark-blas.h
index 3472dd6f6e6326ef0016f56251c8b4d17c36685c..390b17279db2dd153172b7fcb6c294e0a6969d9b 100644
--- a/src/Benchmarks/BLAS/tnl-benchmark-blas.h
+++ b/src/Benchmarks/BLAS/tnl-benchmark-blas.h
@@ -42,7 +42,7 @@ runBlasBenchmarks( Benchmark & benchmark,
                            metadata );
    for( std::size_t size = minSize; size <= maxSize; size *= 2 ) {
       benchmark.setMetadataColumns( Benchmark::MetadataColumns({
-         {"size", convertToString( size ) },
+         { "size", convertToString( size ) },
       } ));
       benchmarkArrayOperations< Real >( benchmark, size );
    }
@@ -62,9 +62,9 @@ runBlasBenchmarks( Benchmark & benchmark,
                            metadata );
    for( std::size_t size = minSize; size <= maxSize; size *= 2 ) {
       benchmark.setMetadataColumns( Benchmark::MetadataColumns({
-         {"rows", convertToString( size ) },
-         {"columns", convertToString( size ) },
-         {"elements per row", convertToString( elementsPerRow ) },
+         { "rows", convertToString( size ) },
+         { "columns", convertToString( size ) },
+         { "elements per row", convertToString( elementsPerRow ) },
       } ));
       benchmarkSpmvSynthetic< Real >( benchmark, size, elementsPerRow );
    }
diff --git a/src/Benchmarks/Benchmarks.h b/src/Benchmarks/Benchmarks.h
index ceb6b9c7eb8656925f8c780ce1272d98ee5178b6..559e27ee26fe6c03d1df5d3d76584376f6f0f7ed 100644
--- a/src/Benchmarks/Benchmarks.h
+++ b/src/Benchmarks/Benchmarks.h
@@ -339,7 +339,7 @@ public:
       closeTable();
       writeTitle( title );
       // add loops to metadata
-      metadata["loops"] = String(loops);
+      metadata["loops"] = convertToString(loops);
       writeMetadata( metadata );
    }
 
@@ -488,14 +488,14 @@ Benchmark::MetadataMap getHardwareMetadata()
 {
    const int cpu_id = 0;
    Devices::CacheSizes cacheSizes = Devices::SystemInfo::getCPUCacheSizes( cpu_id );
-   String cacheInfo = String( cacheSizes.L1data ) + ", "
-                       + String( cacheSizes.L1instruction ) + ", "
-                       + String( cacheSizes.L2 ) + ", "
-                       + String( cacheSizes.L3 );
+   String cacheInfo = convertToString( cacheSizes.L1data ) + ", "
+                       + convertToString( cacheSizes.L1instruction ) + ", "
+                       + convertToString( cacheSizes.L2 ) + ", "
+                       + convertToString( cacheSizes.L3 );
 #ifdef HAVE_CUDA
    const int activeGPU = Devices::CudaDeviceInfo::getActiveDevice();
-   const String deviceArch = String( Devices::CudaDeviceInfo::getArchitectureMajor( activeGPU ) ) + "." +
-                             String( Devices::CudaDeviceInfo::getArchitectureMinor( activeGPU ) );
+   const String deviceArch = convertToString( Devices::CudaDeviceInfo::getArchitectureMajor( activeGPU ) ) + "." +
+                             convertToString( Devices::CudaDeviceInfo::getArchitectureMinor( activeGPU ) );
 #endif
    Benchmark::MetadataMap metadata {
        { "host name", Devices::SystemInfo::getHostname() },
@@ -504,25 +504,25 @@ Benchmark::MetadataMap getHardwareMetadata()
        { "system release", Devices::SystemInfo::getSystemRelease() },
        { "start time", Devices::SystemInfo::getCurrentTime() },
 #ifdef HAVE_MPI
-       { "number of MPI processes", String( (Communicators::MpiCommunicator::IsInitialized())
+       { "number of MPI processes", convertToString( (Communicators::MpiCommunicator::IsInitialized())
                                        ? Communicators::MpiCommunicator::GetSize( Communicators::MpiCommunicator::AllGroup )
                                        : 1 ) },
 #endif
-       { "OpenMP enabled", String( Devices::Host::isOMPEnabled() ) },
-       { "OpenMP threads", String( Devices::Host::getMaxThreadsCount() ) },
+       { "OpenMP enabled", convertToString( Devices::Host::isOMPEnabled() ) },
+       { "OpenMP threads", convertToString( Devices::Host::getMaxThreadsCount() ) },
        { "CPU model name", Devices::SystemInfo::getCPUModelName( cpu_id ) },
-       { "CPU cores", String( Devices::SystemInfo::getNumberOfCores( cpu_id ) ) },
-       { "CPU threads per core", String( Devices::SystemInfo::getNumberOfThreads( cpu_id ) / Devices::SystemInfo::getNumberOfCores( cpu_id ) ) },
-       { "CPU max frequency (MHz)", String( Devices::SystemInfo::getCPUMaxFrequency( cpu_id ) / 1e3 ) },
+       { "CPU cores", convertToString( Devices::SystemInfo::getNumberOfCores( cpu_id ) ) },
+       { "CPU threads per core", convertToString( Devices::SystemInfo::getNumberOfThreads( cpu_id ) / Devices::SystemInfo::getNumberOfCores( cpu_id ) ) },
+       { "CPU max frequency (MHz)", convertToString( Devices::SystemInfo::getCPUMaxFrequency( cpu_id ) / 1e3 ) },
        { "CPU cache sizes (L1d, L1i, L2, L3) (kiB)", cacheInfo },
 #ifdef HAVE_CUDA
        { "GPU name", Devices::CudaDeviceInfo::getDeviceName( activeGPU ) },
-       { "GPU architecture", String( deviceArch ) },
-       { "GPU CUDA cores", String( Devices::CudaDeviceInfo::getCudaCores( activeGPU ) ) },
-       { "GPU clock rate (MHz)", String( (double) Devices::CudaDeviceInfo::getClockRate( activeGPU ) / 1e3 ) },
-       { "GPU global memory (GB)", String( (double) Devices::CudaDeviceInfo::getGlobalMemory( activeGPU ) / 1e9 ) },
-       { "GPU memory clock rate (MHz)", String( (double) Devices::CudaDeviceInfo::getMemoryClockRate( activeGPU ) / 1e3 ) },
-       { "GPU memory ECC enabled", String( Devices::CudaDeviceInfo::getECCEnabled( activeGPU ) ) },
+       { "GPU architecture", deviceArch },
+       { "GPU CUDA cores", convertToString( Devices::CudaDeviceInfo::getCudaCores( activeGPU ) ) },
+       { "GPU clock rate (MHz)", convertToString( (double) Devices::CudaDeviceInfo::getClockRate( activeGPU ) / 1e3 ) },
+       { "GPU global memory (GB)", convertToString( (double) Devices::CudaDeviceInfo::getGlobalMemory( activeGPU ) / 1e9 ) },
+       { "GPU memory clock rate (MHz)", convertToString( (double) Devices::CudaDeviceInfo::getMemoryClockRate( activeGPU ) / 1e3 ) },
+       { "GPU memory ECC enabled", convertToString( Devices::CudaDeviceInfo::getECCEnabled( activeGPU ) ) },
 #endif
    };
 
diff --git a/src/Benchmarks/DistSpMV/tnl-benchmark-distributed-spmv.h b/src/Benchmarks/DistSpMV/tnl-benchmark-distributed-spmv.h
index ecc001d6676c5c8021c3e115ed2af49d49bab614..738fda0566c3cce187005427008391d3118d72c2 100644
--- a/src/Benchmarks/DistSpMV/tnl-benchmark-distributed-spmv.h
+++ b/src/Benchmarks/DistSpMV/tnl-benchmark-distributed-spmv.h
@@ -176,12 +176,12 @@ struct SpmvBenchmark
       benchmark.newBenchmark( name, metadata );
       benchmark.setMetadataColumns( Benchmark::MetadataColumns({
          // TODO: strip the device
-//         {"matrix type", matrix.getType()},
-         {"rows", String( matrix.getRows() ) },
-         {"columns", String( matrix.getColumns() ) },
+//         { "matrix type", matrix.getType() },
+         { "rows", convertToString( matrix.getRows() ) },
+         { "columns", convertToString( matrix.getColumns() ) },
          // FIXME: getMaxRowLengths() returns 0 for matrices loaded from file
-//         {"max elements per row", matrix.getMaxRowLength()},
-         {"max elements per row", String( maxRowLength ) },
+//         { "max elements per row", matrix.getMaxRowLength() },
+         { "max elements per row", convertToString( maxRowLength ) },
       } ));
 
       const bool reorder = parameters.getParameter< bool >( "reorder-dofs" );
diff --git a/src/Benchmarks/HeatEquation/tnlTestGrid2D.h b/src/Benchmarks/HeatEquation/tnlTestGrid2D.h
index afe284ad7c2951f364082d97e78e1ec9a79a895a..084d6cc39a6a755b5ead53d791d22d2c327b37b9 100644
--- a/src/Benchmarks/HeatEquation/tnlTestGrid2D.h
+++ b/src/Benchmarks/HeatEquation/tnlTestGrid2D.h
@@ -214,11 +214,11 @@ template< typename Real,
           typename Index >
 String Meshes::Grid< 2, Real, Device, Index > :: getType()
 {
-   return TNL::String( "Meshes::Grid< " ) +
-          TNL::String( getMeshDimension() ) + ", " +
-          TNL::String( ::getType< RealType >() ) + ", " +
-          TNL::String( Device :: getDeviceType() ) + ", " +
-          TNL::String( ::getType< IndexType >() ) + " >";
+   return String( "Meshes::Grid< " ) +
+          convertToString( getMeshDimension() ) + ", " +
+          String( ::getType< RealType >() ) + ", " +
+          String( Device :: getDeviceType() ) + ", " +
+          String( ::getType< IndexType >() ) + " >";
 }
 
 template< typename Real,
@@ -979,11 +979,11 @@ template< typename Real,
           typename Index >
 String Meshes::Grid< 2, Real, Device, Index > :: getType()
 {
-   return TNL::String( "Meshes::Grid< " ) +
-          TNL::String( getMeshDimension() ) + ", " +
-          TNL::String( ::getType< RealType >() ) + ", " +
-          TNL::String( Device :: getDeviceType() ) + ", " +
-          TNL::String( ::getType< IndexType >() ) + " >";
+   return String( "Meshes::Grid< " ) +
+          convertToString( getMeshDimension() ) + ", " +
+          String( ::getType< RealType >() ) + ", " +
+          String( Device :: getDeviceType() ) + ", " +
+          String( ::getType< IndexType >() ) + " >";
 }
 
 template< typename Real,
diff --git a/src/Benchmarks/LinearSolvers/tnl-benchmark-linear-solvers.h b/src/Benchmarks/LinearSolvers/tnl-benchmark-linear-solvers.h
index c31f776cd4ff571b4f00e85a6ffcef2959a55e50..ce8d49ae0864a4c414eb10f93d1d7aae45783810 100644
--- a/src/Benchmarks/LinearSolvers/tnl-benchmark-linear-solvers.h
+++ b/src/Benchmarks/LinearSolvers/tnl-benchmark-linear-solvers.h
@@ -188,7 +188,7 @@ benchmarkIterativeSolvers( Benchmark& benchmark,
          benchmark.setOperation("BiCGstab (Jacobi)");
          for( int ell = 1; ell <= ell_max; ell++ ) {
             parameters.template setParameter< int >( "bicgstab-ell", ell );
-            benchmark.setOperation("BiCGstab(" + String(ell) + ") (Jacobi)");
+            benchmark.setOperation("BiCGstab(" + convertToString(ell) + ") (Jacobi)");
             benchmarkSolver< BICGStabL, Diagonal >( benchmark, parameters, matrixPointer, x0, b );
             #ifdef HAVE_CUDA
             benchmarkSolver< BICGStabL, Diagonal >( benchmark, parameters, cudaMatrixPointer, cuda_x0, cuda_b );
@@ -244,7 +244,7 @@ benchmarkIterativeSolvers( Benchmark& benchmark,
       if( solvers.count( "bicgstab-ell" ) ) {
          for( int ell = 1; ell <= ell_max; ell++ ) {
             parameters.template setParameter< int >( "bicgstab-ell", ell );
-            benchmark.setOperation("BiCGstab(" + String(ell) + ") (ILU0)");
+            benchmark.setOperation("BiCGstab(" + convertToString(ell) + ") (ILU0)");
             benchmarkSolver< BICGStabL, ILU0 >( benchmark, parameters, matrixPointer, x0, b );
             #ifdef HAVE_CUDA
             benchmarkSolver< BICGStabL, ILU0 >( benchmark, parameters, cudaMatrixPointer, cuda_x0, cuda_b );
@@ -300,7 +300,7 @@ benchmarkIterativeSolvers( Benchmark& benchmark,
       if( solvers.count( "bicgstab-ell" ) ) {
          for( int ell = 1; ell <= ell_max; ell++ ) {
             parameters.template setParameter< int >( "bicgstab-ell", ell );
-            benchmark.setOperation("BiCGstab(" + String(ell) + ") (ILUT)");
+            benchmark.setOperation("BiCGstab(" + convertToString(ell) + ") (ILUT)");
             benchmarkSolver< BICGStabL, ILUT >( benchmark, parameters, matrixPointer, x0, b );
             #ifdef HAVE_CUDA
             benchmarkSolver< BICGStabL, ILUT >( benchmark, parameters, cudaMatrixPointer, cuda_x0, cuda_b );
@@ -346,12 +346,12 @@ struct LinearSolversBenchmark
       benchmark.newBenchmark( name, metadata );
       benchmark.setMetadataColumns( Benchmark::MetadataColumns({
          // TODO: strip the device
-//         {"matrix type", matrixPointer->getType()},
-         {"rows", String( matrixPointer->getRows() ) },
-         {"columns", String( matrixPointer->getColumns() ) },
+//         { "matrix type", matrixPointer->getType() },
+         { "rows", convertToString( matrixPointer->getRows() ) },
+         { "columns", convertToString( matrixPointer->getColumns() ) },
          // FIXME: getMaxRowLengths() returns 0 for matrices loaded from file
-//         {"max elements per row", matrixPointer->getMaxRowLength()},
-         {"max elements per row", String( maxRowLength ) },
+//         { "max elements per row", matrixPointer->getMaxRowLength() },
+         { "max elements per row", convertToString( maxRowLength ) },
       } ));
 
       const bool reorder = parameters.getParameter< bool >( "reorder-dofs" );
diff --git a/src/Examples/StringExample.cpp b/src/Examples/StringExample.cpp
index f69fe9f1f70a1996892228600c9062855d6d0f40..3db23e6a1b9ac02108de82689acd8a9e50a54288 100644
--- a/src/Examples/StringExample.cpp
+++ b/src/Examples/StringExample.cpp
@@ -12,7 +12,7 @@ int main( int argc, char* argv[] )
     String str1;
     String str2( "xxstringxxx", 2, 3 );
     String str3( str2 );                    // copy constructor
-    String str4( 28.4 );                    // converts to string
+    String str4 = convertToString( 28.4 );  // converts to string
 
     cout << "str1:" << str1 << endl;
     cout << "str2:" << str2 << endl;
@@ -93,7 +93,7 @@ int main( int argc, char* argv[] )
     cout << "h:" << h << endl;
 
     String i;
-    i = 'a' + 'b';
+    i = convertToString( 'a' ) + 'b';
     cout << "i:" << i << endl;
 
     String letter1( "u" );
diff --git a/src/Examples/transport-equation/transportEquationProblemEoc_impl.h b/src/Examples/transport-equation/transportEquationProblemEoc_impl.h
index 4818188774c2ceedb53266e54367e371251e51ac..512e310d2f62ac5e118a729db9a1c5ae775bef89 100644
--- a/src/Examples/transport-equation/transportEquationProblemEoc_impl.h
+++ b/src/Examples/transport-equation/transportEquationProblemEoc_impl.h
@@ -89,7 +89,7 @@ setup( const Config::ParameterContainer& parameters,
             return false;
          Containers::StaticVector< Dimension, RealType > velocity;
          for( int i = 0; i < Dimension; i++ )
-            velocity[ i ] = parameters.getParameter< double >( "velocity-field-" + String( i ) + "-constant" );
+            velocity[ i ] = parameters.getParameter< double >( "velocity-field-" + convertToString( i ) + "-constant" );
 
          Functions::MeshFunctionEvaluator< MeshFunction, ExactSolutionType > evaluator;
          RealType time( 0.0 );
diff --git a/src/Python/pytnl/tnl/String.cpp b/src/Python/pytnl/tnl/String.cpp
index 309a6fe25fdafae45c672cd321ad851a55f57056..551f94ddf61f3e492dbeefb2b140d570dd779c6f 100644
--- a/src/Python/pytnl/tnl/String.cpp
+++ b/src/Python/pytnl/tnl/String.cpp
@@ -19,8 +19,8 @@ void export_String( py::module & m )
         .def(py::init<const char*>())
         .def(py::init<const char*, int>())
         .def(py::init<const char*, int, int>())
-        .def(py::init<int>())
-        .def(py::init<double>())
+        .def(py::init([](int v){ return TNL::convertToString(v); }))
+        .def(py::init([](double v){ return TNL::convertToString(v); }))
         .def_static("getType", &TNL::String::getType)
         // __str__ (uses operator<<)
         // explicit namespace resolution is necessary, see http://stackoverflow.com/a/3084341/4180822
diff --git a/src/TNL/Containers/MultiVector1D_impl.h b/src/TNL/Containers/MultiVector1D_impl.h
index e8f42c5391774360f6af595c6e47d2b329e7c1de..5ac452c2929a5717d37d726aa1778bf13db77921 100644
--- a/src/TNL/Containers/MultiVector1D_impl.h
+++ b/src/TNL/Containers/MultiVector1D_impl.h
@@ -22,7 +22,7 @@ template< typename Real, typename Device, typename Index >
 String MultiVector< 1, Real, Device, Index > :: getType()
 {
    return String( "Containers::MultiVector< ") +
-          String( Dimension ) +
+          convertToString( Dimension ) +
           String( ", " ) +
           String( TNL::getType< Real >() ) +
           String( ", " ) +
diff --git a/src/TNL/Containers/MultiVector2D_impl.h b/src/TNL/Containers/MultiVector2D_impl.h
index 2c39f22226a9ad5f070505f144e1811ac19e18ca..7f061ad06cf9e0288d465ab3aa775855374ddd98 100644
--- a/src/TNL/Containers/MultiVector2D_impl.h
+++ b/src/TNL/Containers/MultiVector2D_impl.h
@@ -22,7 +22,7 @@ template< typename Real, typename Device, typename Index >
 String MultiVector< 2, Real, Device, Index > :: getType()
 {
    return String( "Containers::MultiVector< ") +
-          String( Dimension ) +
+          convertToString( Dimension ) +
           String( ", " ) +
           String( TNL::getType< Real >() ) +
           String( ", " ) +
diff --git a/src/TNL/Containers/MultiVector3D_impl.h b/src/TNL/Containers/MultiVector3D_impl.h
index cd4e543cec48c96464c2775d5ad971791f6ae221..c7949014d7233bc14d744457201d14e7923a70fe 100644
--- a/src/TNL/Containers/MultiVector3D_impl.h
+++ b/src/TNL/Containers/MultiVector3D_impl.h
@@ -22,7 +22,7 @@ template< typename Real, typename Device, typename Index >
 String MultiVector< 3, Real, Device, Index > :: getType()
 {
    return String( "Containers::MultiVector< ") +
-          String( Dimension ) +
+          convertToString( Dimension ) +
           String( ", " ) +
           String( TNL::getType< Real >() ) +
           String( ", " ) +
diff --git a/src/TNL/Containers/MultiVector4D_impl.h b/src/TNL/Containers/MultiVector4D_impl.h
index 6fe5a4a062eca65d83adfe10537b79d77af5f449..14708ec20c6d7c4daa5cb1424843bb34fcd78aa9 100644
--- a/src/TNL/Containers/MultiVector4D_impl.h
+++ b/src/TNL/Containers/MultiVector4D_impl.h
@@ -22,7 +22,7 @@ template< typename Real, typename Device, typename Index >
 String MultiVector< 4, Real, Device, Index > :: getType()
 {
    return String( "Containers::MultiVector< ") +
-          String( Dimension ) +
+          convertToString( Dimension ) +
           String( ", " ) +
           String( TNL::getType< Real >() ) +
           String( ", " ) +
diff --git a/src/TNL/Containers/StaticArray1D_impl.h b/src/TNL/Containers/StaticArray1D_impl.h
index 3fd54145053bffb24e2ab4219e694102853b3165..81f5a08d24c01780a3ba5e96757399a96d4e746f 100644
--- a/src/TNL/Containers/StaticArray1D_impl.h
+++ b/src/TNL/Containers/StaticArray1D_impl.h
@@ -48,7 +48,7 @@ template< typename Value >
 String StaticArray< 1, Value >::getType()
 {
    return String( "Containers::StaticArray< " ) +
-          String( size ) +
+          convertToString( size ) +
           String( ", " ) +
           TNL::getType< Value >() +
           String( " >" );
diff --git a/src/TNL/Containers/StaticArray2D_impl.h b/src/TNL/Containers/StaticArray2D_impl.h
index 841c89529aa55571f0446eb2a7d0895b21aecf69..55096abd08da4b319f3e59bbb2b5445be2249723 100644
--- a/src/TNL/Containers/StaticArray2D_impl.h
+++ b/src/TNL/Containers/StaticArray2D_impl.h
@@ -60,7 +60,7 @@ template< typename Value >
 String StaticArray< 2, Value >::getType()
 {
    return String( "Containers::StaticArray< " ) +
-          String( size ) +
+          convertToString( size ) +
           String( ", " ) +
           TNL::getType< Value >() +
           String( " >" );
diff --git a/src/TNL/Containers/StaticArray3D_impl.h b/src/TNL/Containers/StaticArray3D_impl.h
index 1ed6d2c155f7e0d5d170d12ba8c426adca41b52d..1aac8cc890b0ba46572e1fffca4a53616cb20f11 100644
--- a/src/TNL/Containers/StaticArray3D_impl.h
+++ b/src/TNL/Containers/StaticArray3D_impl.h
@@ -64,7 +64,7 @@ template< typename Value >
 String StaticArray< 3, Value >::getType()
 {
    return String( "Containers::StaticArray< " ) +
-          String( size ) +
+          convertToString( size ) +
           String( ", " ) +
           TNL::getType< Value >() +
           String( " >" );
diff --git a/src/TNL/Containers/StaticArray_impl.h b/src/TNL/Containers/StaticArray_impl.h
index 898bc9bd5625ba73b77c015d0472337a0eeda81f..0917b0f1cb9019665a3b0f829953ecf45f677d66 100644
--- a/src/TNL/Containers/StaticArray_impl.h
+++ b/src/TNL/Containers/StaticArray_impl.h
@@ -52,7 +52,7 @@ template< int Size, typename Value >
 String StaticArray< Size, Value >::getType()
 {
    return String( "Containers::StaticArray< " ) +
-          String( Size ) +
+          convertToString( Size ) +
           String( ", " ) +
           TNL::getType< Value >() +
           String( " >" );
diff --git a/src/TNL/Containers/StaticVector1D_impl.h b/src/TNL/Containers/StaticVector1D_impl.h
index 8045d12ac680c802bacb959842a0bc2b0ffe22e2..9eb2d90c01692600d9e7ae7c3a633037b1d5db59 100644
--- a/src/TNL/Containers/StaticVector1D_impl.h
+++ b/src/TNL/Containers/StaticVector1D_impl.h
@@ -56,7 +56,7 @@ template< typename Real >
 String StaticVector< 1, Real >::getType()
 {
    return String( "Containers::StaticVector< " ) +
-          String( 1 ) +
+          convertToString( 1 ) +
           String( ", " ) +
           TNL::getType< Real >() +
           String( " >" );
diff --git a/src/TNL/Containers/StaticVector2D_impl.h b/src/TNL/Containers/StaticVector2D_impl.h
index 8691508b81557b6ce448ca24d65df2b2089bc035..0a8cb3ec0be4a23919a121fb29d8d31511b58a65 100644
--- a/src/TNL/Containers/StaticVector2D_impl.h
+++ b/src/TNL/Containers/StaticVector2D_impl.h
@@ -64,9 +64,9 @@ template< typename Real >
 String StaticVector< 2, Real >::getType()
 {
    return String( "Containers::StaticVector< " ) +
-          String( 2 ) +
+          convertToString( 2 ) +
           String( ", " ) +
-         TNL::getType< Real >() +
+          TNL::getType< Real >() +
           String( " >" );
 }
 
diff --git a/src/TNL/Containers/StaticVector3D_impl.h b/src/TNL/Containers/StaticVector3D_impl.h
index 1e2a44cfbc29caa97f12fb3e3b0d0b417cb31458..77f1893f66b60cddc032099435a095b5a0abf09f 100644
--- a/src/TNL/Containers/StaticVector3D_impl.h
+++ b/src/TNL/Containers/StaticVector3D_impl.h
@@ -65,9 +65,9 @@ template< typename Real >
 String StaticVector< 3, Real >::getType()
 {
    return String( "Containers::StaticVector< " ) +
-          String( 3 ) +
+          convertToString( 3 ) +
           String( ", " ) +
-         TNL::getType< Real >() +
+          TNL::getType< Real >() +
           String( " >" );
 }
 
diff --git a/src/TNL/Containers/StaticVector_impl.h b/src/TNL/Containers/StaticVector_impl.h
index bfb473c92f8440ad941869a39ec933d85025f27c..09fbcc34d392fcccd9252860d86a11d05f4828e4 100644
--- a/src/TNL/Containers/StaticVector_impl.h
+++ b/src/TNL/Containers/StaticVector_impl.h
@@ -49,7 +49,7 @@ StaticVector< Size, Real >::setup( const Config::ParameterContainer& parameters,
                                    const String& prefix )
 {
    for( int i = 0; i < Size; i++ )
-      if( ! parameters.template getParameter< double >( prefix + String( i ), this->data[ i ] ) )
+      if( ! parameters.template getParameter< double >( prefix + convertToString( i ), this->data[ i ] ) )
          return false;
    return true;
 }
@@ -58,7 +58,7 @@ template< int Size, typename Real >
 String StaticVector< Size, Real >::getType()
 {
    return String( "Containers::StaticVector< " ) +
-          String( Size ) +
+          convertToString( Size ) +
           String( ", " ) +
           TNL::getType< Real >() +
           String( " >" );
diff --git a/src/TNL/Devices/CudaDeviceInfo.cu b/src/TNL/Devices/CudaDeviceInfo.cu
index 56905df9675ef10b07ba40d1876215376ade611c..4e66c095d6579385f668de4cf93b255b3182c87f 100644
--- a/src/TNL/Devices/CudaDeviceInfo.cu
+++ b/src/TNL/Devices/CudaDeviceInfo.cu
@@ -198,8 +198,8 @@ writeDeviceInfo( Logger& logger )
 //      logger.writeParameter< int >( "Device no.", i, 1 );
       int i = getActiveDevice();
       logger.writeParameter< String >( "Name", getDeviceName( i ), 2 );
-      String deviceArch = String( getArchitectureMajor( i ) ) + "." +
-                              String( getArchitectureMinor( i ) );
+      String deviceArch = convertToString( getArchitectureMajor( i ) ) + "." +
+                          convertToString( getArchitectureMinor( i ) );
       logger.writeParameter< String >( "Architecture", deviceArch, 2 );
       logger.writeParameter< int >( "CUDA cores", getCudaCores( i ), 2 );
       double clockRate = ( double ) getClockRate( i ) / 1.0e3;
diff --git a/src/TNL/Devices/SystemInfo.cpp b/src/TNL/Devices/SystemInfo.cpp
index 490f65f101c762c96dc0c6a5bf281a1ef232d7e5..377922b26e320db704fe327050e93e77de932ada 100644
--- a/src/TNL/Devices/SystemInfo.cpp
+++ b/src/TNL/Devices/SystemInfo.cpp
@@ -118,7 +118,7 @@ int
 SystemInfo::getCPUMaxFrequency( int cpu_id )
 {
    String fileName( "/sys/devices/system/cpu/cpu" );
-   fileName += String( cpu_id ) + "/cpufreq/cpuinfo_max_freq";
+   fileName += convertToString( cpu_id ) + "/cpufreq/cpuinfo_max_freq";
    return readFile< int >( fileName );
 }
 
@@ -126,11 +126,11 @@ CacheSizes
 SystemInfo::getCPUCacheSizes( int cpu_id )
 {
    String directory( "/sys/devices/system/cpu/cpu" );
-   directory += String( cpu_id ) + "/cache";
+   directory += convertToString( cpu_id ) + "/cache";
 
    CacheSizes sizes;
    for( int i = 0; i <= 3; i++ ) {
-      const String cache = directory + "/index" + String( i );
+      const String cache = directory + "/index" + convertToString( i );
 
       // check if the directory exists
       struct stat st;
@@ -175,10 +175,10 @@ writeDeviceInfo( Logger& logger )
    logger.writeParameter< int >( "Threads per core:", threadsPerCore, 1 );
    logger.writeParameter< float >( "Max clock rate (in MHz):", getCPUMaxFrequency( cpu_id ) / 1000, 1 );
    CacheSizes cacheSizes = getCPUCacheSizes( cpu_id );
-   String cacheInfo = String( cacheSizes.L1data ) + ", "
-                       + String( cacheSizes.L1instruction ) + ", "
-                       + String( cacheSizes.L2 ) + ", "
-                       + String( cacheSizes.L3 );
+   String cacheInfo = convertToString( cacheSizes.L1data ) + ", "
+                       + convertToString( cacheSizes.L1instruction ) + ", "
+                       + convertToString( cacheSizes.L2 ) + ", "
+                       + convertToString( cacheSizes.L3 );
    logger.writeParameter< String >( "Cache (L1d, L1i, L2, L3):", cacheInfo, 1 );
 }
 
diff --git a/src/TNL/Functions/MeshFunction_impl.h b/src/TNL/Functions/MeshFunction_impl.h
index 3a8c74b6785b68357707ff9e7349a42a67e07f5f..49b75d52fdbdb14eca36cd9d5b543fb838f4426c 100644
--- a/src/TNL/Functions/MeshFunction_impl.h
+++ b/src/TNL/Functions/MeshFunction_impl.h
@@ -102,7 +102,7 @@ getType()
 {
    return String( "Functions::MeshFunction< " ) +
                      Mesh::getType() + ", " +
-                     String( MeshEntityDimension ) + ", " +
+                     convertToString( MeshEntityDimension ) + ", " +
                     TNL::getType< Real >() +
                      " >";
 };
@@ -126,7 +126,7 @@ getSerializationType()
 {
    return String( "Functions::MeshFunction< " ) +
                      Mesh::getSerializationType() + ", " +
-                     String( MeshEntityDimension ) + ", " +
+                     convertToString( MeshEntityDimension ) + ", " +
                     TNL::getType< Real >() +
                      " >";
 };
diff --git a/src/TNL/Functions/VectorField.h b/src/TNL/Functions/VectorField.h
index a873165b401fa4f8dc10c7c6fac31682cb81dd2b..46fdffcba1ffe34d1a57f75ad8b6b1474fbefb5e 100644
--- a/src/TNL/Functions/VectorField.h
+++ b/src/TNL/Functions/VectorField.h
@@ -36,7 +36,7 @@ class VectorField
                                const String& prefix = "" )
       {
          for( int i = 0; i < Size; i++ )
-            FunctionType::configSetup( config, prefix + String( i ) + "-" );
+            FunctionType::configSetup( config, prefix + convertToString( i ) + "-" );
       }
 
       template< typename MeshPointer >
@@ -45,7 +45,7 @@ class VectorField
                   const String& prefix = "" )
       {
          for( int i = 0; i < Size; i++ )
-            if( ! vectorField[ i ].setup( parameters, prefix + String( i ) + "-" ) )
+            if( ! vectorField[ i ].setup( parameters, prefix + convertToString( i ) + "-" ) )
             {
                std::cerr << "Unable to setup " << i << "-th coordinate of the vector field." << std::endl;
                return false;
@@ -103,7 +103,7 @@ class VectorField< Size, MeshFunction< Mesh, MeshEntityDimension, Real > >
                                const String& prefix = "" )
       {
          for( int i = 0; i < Size; i++ )
-            FunctionType::configSetup( config, prefix + String( i ) + "-" );
+            FunctionType::configSetup( config, prefix + convertToString( i ) + "-" );
       }
       
       VectorField() {};
@@ -117,7 +117,7 @@ class VectorField< Size, MeshFunction< Mesh, MeshEntityDimension, Real > >
       static String getType()
       {
          return String( "Functions::VectorField< " ) +
-                  String( Size) + ", " +
+                  convertToString( Size) + ", " +
                  FunctionType::getType() +
                   " >";
       }
@@ -130,7 +130,7 @@ class VectorField< Size, MeshFunction< Mesh, MeshEntityDimension, Real > >
       static String getSerializationType()
       {
          return String( "Functions::VectorField< " ) +
-                  String( Size) + ", " +
+                  convertToString( Size) + ", " +
                  FunctionType::getSerializationType() +
                   " >";         
       }
@@ -164,7 +164,7 @@ class VectorField< Size, MeshFunction< Mesh, MeshEntityDimension, Real > >
                   const String& prefix = "" )
       {
          for( int i = 0; i < Size; i++ )
-            if( ! vectorField[ i ].setup( meshPointer, parameters, prefix + String( i ) + "-" ) )
+            if( ! vectorField[ i ].setup( meshPointer, parameters, prefix + convertToString( i ) + "-" ) )
             {
                std::cerr << "Unable to setup " << i << "-th coordinate of the vector field." << std::endl;
                return false;
diff --git a/src/TNL/Meshes/DefaultConfig.h b/src/TNL/Meshes/DefaultConfig.h
index 147a9ab10b911ba0a0bca9ec1dd3b74035508e6e..5e8a7cbef85fc2a03681553f7348af5c95f45dbb 100644
--- a/src/TNL/Meshes/DefaultConfig.h
+++ b/src/TNL/Meshes/DefaultConfig.h
@@ -50,7 +50,7 @@ struct DefaultConfig
    {
       return String( "Meshes::DefaultConfig< " ) +
              Cell::getType() + ", " +
-             String( WorldDimension ) + ", " +
+             convertToString( WorldDimension ) + ", " +
              TNL::getType< Real >() + ", " +
              TNL::getType< GlobalIndex >() + ", " +
              TNL::getType< LocalIndex >() + ", " +
diff --git a/src/TNL/Meshes/GridDetails/Grid1D_impl.h b/src/TNL/Meshes/GridDetails/Grid1D_impl.h
index 99e456112366547368cccb03c5a240e01583a534..1754edc587fee6202d59f778cb6c9485d3a05f4e 100644
--- a/src/TNL/Meshes/GridDetails/Grid1D_impl.h
+++ b/src/TNL/Meshes/GridDetails/Grid1D_impl.h
@@ -39,7 +39,7 @@ template< typename Real,
 String Grid< 1, Real, Device, Index >::getType()
 {
    return String( "Meshes::Grid< " ) +
-          String( getMeshDimension() ) + ", " +
+          convertToString( getMeshDimension() ) + ", " +
           String( TNL::getType< RealType >() ) + ", " +
           String( Device::getDeviceType() ) + ", " +
           String( TNL::getType< IndexType >() ) + " >";
diff --git a/src/TNL/Meshes/GridDetails/Grid2D_impl.h b/src/TNL/Meshes/GridDetails/Grid2D_impl.h
index 15874efd502bb07bf157561e0324d6c992470929..b315d5d086aee7532817edd67b9870735d4a49a5 100644
--- a/src/TNL/Meshes/GridDetails/Grid2D_impl.h
+++ b/src/TNL/Meshes/GridDetails/Grid2D_impl.h
@@ -42,7 +42,7 @@ template< typename Real,
 String Grid< 2, Real, Device, Index > :: getType()
 {
    return String( "Meshes::Grid< " ) +
-          String( getMeshDimension() ) + ", " +
+          convertToString( getMeshDimension() ) + ", " +
           String( TNL::getType< RealType >() ) + ", " +
           String( Device :: getDeviceType() ) + ", " +
           String( TNL::getType< IndexType >() ) + " >";
diff --git a/src/TNL/Meshes/GridDetails/Grid3D_impl.h b/src/TNL/Meshes/GridDetails/Grid3D_impl.h
index e802be7df9ff79acd5ae447d5f976664566c3053..cc6805ac0632de43899d124c87fe4427f84487e5 100644
--- a/src/TNL/Meshes/GridDetails/Grid3D_impl.h
+++ b/src/TNL/Meshes/GridDetails/Grid3D_impl.h
@@ -49,7 +49,7 @@ template< typename Real,
 String Grid< 3, Real, Device, Index > :: getType()
 {
    return String( "Meshes::Grid< " ) +
-          String( getMeshDimension() ) + ", " +
+          convertToString( getMeshDimension() ) + ", " +
           String( TNL::getType< RealType >() ) + ", " +
           String( Device :: getDeviceType() ) + ", " +
           String( TNL::getType< IndexType >() ) + " >";
diff --git a/src/TNL/String.cpp b/src/TNL/String.cpp
index 92663a4d8aed06405514f4a9e2ca69013832a92a..d814a662c32ab562cefbddac714186366568b5f4 100644
--- a/src/TNL/String.cpp
+++ b/src/TNL/String.cpp
@@ -240,7 +240,7 @@ String String::operator+( char str ) const
 
 bool String::operator==( char str ) const
 {
-   return *this == String( str );
+   return *this == convertToString( str );
 }
 
 bool String::operator!=( char str ) const
@@ -424,7 +424,7 @@ bool String :: getLine( std::istream& stream )
 
 String operator+( char string1, const String& string2 )
 {
-   return String( string1 ) + string2;
+   return convertToString( string1 ) + string2;
 }
 
 String operator+( const char* string1, const String& string2 )
diff --git a/src/TNL/String.h b/src/TNL/String.h
index 44f42423fe207955dab89e05eddf62344191ea19..9e2fb201d0af02d3573d0f03b37c32cddf1e3ee2 100644
--- a/src/TNL/String.h
+++ b/src/TNL/String.h
@@ -67,19 +67,6 @@ class String
       /// @param str Another string object, whose value is copied.
       String( const String& str );
 
-      /// \brief Converts anything to a string.
-      ///
-      /// This function converts any type of value into type string.
-      /// @tparam T is a type of a value to be converted
-      /// @param value Word of any type (e.g. int, bool, double,...).
-      template< typename T >
-      explicit
-      String( T value )
-         : string( nullptr ), length( 0 )
-      {
-         setString( convertToString( value ).getString() );
-      }
-
       /// \brief Destructor.
       ~String();
 
@@ -276,8 +263,6 @@ class String
       /// expression based on the success in reading the line.
       bool getLine( std::istream& stream );
 
-      friend std::ostream& operator<<( std::ostream& stream, const String& str );
-
    protected:
       
       /// \brief Pointer to char ended with zero byte.
diff --git a/src/UnitTests/Containers/ListTest.cpp b/src/UnitTests/Containers/ListTest.cpp
index 3b5fdaecf385dab8da032a020ef6b6511ccf0c18..32e65c22318a4059c981e9fb38bd93de22a2e5da 100644
--- a/src/UnitTests/Containers/ListTest.cpp
+++ b/src/UnitTests/Containers/ListTest.cpp
@@ -16,6 +16,35 @@
 using namespace TNL;
 using namespace TNL::Containers;
 
+// minimal custom data structure usable as ValueType in List
+struct MyData
+{
+   double data;
+
+   __cuda_callable__
+   MyData() : data(0) {}
+
+   template< typename T >
+   __cuda_callable__
+   MyData( T v ) : data(v) {}
+
+   __cuda_callable__
+   bool operator==( const MyData& v ) const { return data == v.data; }
+
+   __cuda_callable__
+   bool operator!=( const MyData& v ) const { return data != v.data; }
+
+   static String getType()
+   {
+      return String( "MyData" );
+   }
+};
+
+std::ostream& operator<<( std::ostream& str, const MyData& v )
+{
+   return str << v.data;
+}
+
 
 // test fixture for typed tests
 template< typename List >
@@ -32,7 +61,7 @@ using ListTypes = ::testing::Types<
    List< long   >,
    List< float  >,
    List< double >,
-   List< String >
+   List< MyData >
 >;
 
 TYPED_TEST_CASE( ListTest, ListTypes );
diff --git a/src/UnitTests/StringTest.cpp b/src/UnitTests/StringTest.cpp
index f6ee1a57225d0287da3418a162363ee39e73925e..389c208e7f83d67a16ff0d70dace341976f55444 100644
--- a/src/UnitTests/StringTest.cpp
+++ b/src/UnitTests/StringTest.cpp
@@ -51,12 +51,12 @@ TEST( StringTest, CopyConstructor )
    EXPECT_EQ( strcmp( emptyString2.getString(), "" ), 0 );
 }
 
-TEST( StringTest, ConstructorWithNumber )
+TEST( StringTest, convertToString )
 {
-   String string1( 10 );
-   String string2( -5 );
-   String string3( true );
-   String string4( false );
+   String string1 = convertToString( 10 );
+   String string2 = convertToString( -5 );
+   String string3 = convertToString( true );
+   String string4 = convertToString( false );
 
    EXPECT_EQ( strcmp( string1.getString(), "10" ), 0 );
    EXPECT_EQ( strcmp( string2.getString(), "-5" ), 0 );