[C++] use constexpr to define precedence checks lookup tables

Author: nbradac

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/cpp/CppGenerator.java

@@ -243,7 +243,6 @@ public void generate() throws IOException
                 generateDisplay(sb, msgToken.name(), fields, groups, varData);
                 sb.append(generateMessageLength(groups, varData, BASE_INDENT));
                 sb.append("};\n");
-                generateLookupTableDefinitions(sb, className, fieldPrecedenceModel);
                 sb.append(CppUtil.closingBraces(namespaces.length)).append("#endif\n");
                 out.append(sb);
             }
@@ -2975,12 +2974,8 @@ private static CharSequence generateLookupTableDeclarations(final FieldPrecedenc
         }
 
         final StringBuilder sb = new StringBuilder();
-        sb.append(INDENT).append("static const std::string STATE_NAME_LOOKUP[")
-            .append(fieldPrecedenceModel.stateCount())
-            .append("];\n");
-        sb.append(INDENT).append("static const std::string STATE_TRANSITIONS_LOOKUP[")
-            .append(fieldPrecedenceModel.stateCount())
-            .append("];\n\n");
+
+        generateLookupTableDefinitions(sb, fieldPrecedenceModel);
 
         sb.append(INDENT).append("static std::string codecStateName(CodecState state)\n")
             .append(INDENT).append("{\n")
@@ -2997,27 +2992,24 @@ private static CharSequence generateLookupTableDeclarations(final FieldPrecedenc
 
     private static void generateLookupTableDefinitions(
         final StringBuilder sb,
-        final String className,
         final FieldPrecedenceModel fieldPrecedenceModel)
     {
         if (null == fieldPrecedenceModel)
         {
             return;
         }
 
-        sb.append("\n").append("const std::string ").append(className).append("::STATE_NAME_LOOKUP[")
-            .append(fieldPrecedenceModel.stateCount()).append("] =\n")
-            .append("{\n");
+        sb.append(INDENT).append("static constexpr const char *STATE_NAME_LOOKUP[] =\n")
+            .append(INDENT).append("{\n");
         fieldPrecedenceModel.forEachStateOrderedByStateNumber((state) ->
-            sb.append(INDENT).append("\"").append(state.name()).append("\",\n"));
-        sb.append("};\n\n");
+            sb.append(INDENT).append(INDENT).append("\"").append(state.name()).append("\",\n"));
+        sb.append(INDENT).append("};\n\n");
 
-        sb.append("const std::string ").append(className).append("::STATE_TRANSITIONS_LOOKUP[")
-            .append(fieldPrecedenceModel.stateCount()).append("] =\n")
-            .append("{\n");
+        sb.append(INDENT).append("static constexpr const char *STATE_TRANSITIONS_LOOKUP[] =\n")
+            .append(INDENT).append("{\n");
         fieldPrecedenceModel.forEachStateOrderedByStateNumber((state) ->
         {
-            sb.append(INDENT).append("\"");
+            sb.append(INDENT).append(INDENT).append("\"");
             final MutableBoolean isFirst = new MutableBoolean(true);
             final Set<String> transitionDescriptions = new HashSet<>();
             fieldPrecedenceModel.forEachTransitionFrom(state, (transitionGroup) ->
@@ -3038,7 +3030,7 @@ private static void generateLookupTableDefinitions(
             });
             sb.append("\",\n");
         });
-        sb.append("};\n\n");
+        sb.append(INDENT).append("};\n\n");
     }
 
     private static CharSequence qualifiedStateCase(final FieldPrecedenceModel.State state)

sbe-tool/src/test/java/uk/co/real_logic/sbe/generation/cpp/CppGeneratorTest.java

@@ -114,4 +114,30 @@ void dtosShouldReferenceTypesInDifferentPackages() throws Exception
             assertThat(source, containsString("using namespace test::message::schema::common;"));
         }
     }
+
+    @Test
+    void shouldUseConstexprWhenDefiningPrecedenceChecksLookupTables() throws Exception
+    {
+        try (InputStream in = Tests.getLocalResource("code-generation-schema.xml"))
+        {
+            final ParserOptions options = ParserOptions.builder().stopOnError(true).build();
+            final MessageSchema schema = parse(in, options);
+            final IrGenerator irg = new IrGenerator();
+            final Ir ir = irg.generate(schema);
+            final StringWriterOutputManager outputManager = new StringWriterOutputManager();
+            outputManager.setPackageName(ir.applicableNamespace());
+
+            final CppGenerator generator = new CppGenerator(
+                ir,
+                false,
+                PrecedenceChecks.newInstance(new PrecedenceChecks.Context().shouldGeneratePrecedenceChecks(true)),
+                false,
+                outputManager);
+            generator.generate();
+
+            final String source = outputManager.getSource("code.generation.test.Car").toString();
+            assertThat(source, containsString("static constexpr const char *STATE_NAME_LOOKUP[] ="));
+            assertThat(source, containsString("static constexpr const char *STATE_TRANSITIONS_LOOKUP[] ="));
+        }
+    }
 }