Added conversion operations that can be used inline in JSON.

e.g.: { myfield: cos(rad(180)) } is equivalent to writing { myfield: -1.0 }

Bug: 29338398
Change-Id: I6fc4ef1fd10bda3ba78cba464414dd071a2f50ca
Tested: on Linux.

tests/test.cpp

@@ -814,20 +814,29 @@ void ErrorTest() {
   TestError("table X { Y:byte; } root_type X; { Y:1, Y:2 }", "more than once");
 }
 
-// Additional parser testing not covered elsewhere.
-void ScientificTest() {
+float TestValue(const char *json) {
   flatbuffers::Parser parser;
 
   // Simple schema.
   TEST_EQ(parser.Parse("table X { Y:float; } root_type X;"), true);
 
-  // Test scientific notation numbers.
-  TEST_EQ(parser.Parse("{ Y:0.0314159e+2 }"), true);
+  TEST_EQ(parser.Parse(json), true);
   auto root = flatbuffers::GetRoot<float>(parser.builder_.GetBufferPointer());
   // root will point to the table, which is a 32bit vtable offset followed
   // by a float:
-  TEST_EQ(sizeof(flatbuffers::soffset_t) == 4 &&  // Test assumes 32bit offsets
-          fabs(root[1] - 3.14159) < 0.001, true);
+  TEST_EQ(sizeof(flatbuffers::soffset_t), 4);  // Test assumes 32bit offsets
+  return root[1];
+}
+
+bool FloatCompare(float a, float b) { return fabs(a - b) < 0.001; }
+
+// Additional parser testing not covered elsewhere.
+void ValueTest() {
+  // Test scientific notation numbers.
+  TEST_EQ(FloatCompare(TestValue("{ Y:0.0314159e+2 }"), 3.14159), true);
+
+  // Test conversion functions.
+  TEST_EQ(FloatCompare(TestValue("{ Y:cos(rad(180)) }"), -1), true);
 }
 
 void EnumStringsTest() {
@@ -963,7 +972,7 @@ int main(int /*argc*/, const char * /*argv*/[]) {
   FuzzTest2();
 
   ErrorTest();
-  ScientificTest();
+  ValueTest();
   EnumStringsTest();
   IntegerOutOfRangeTest();
   UnicodeTest();