This is a C++11 header-only library for dynamically typed objects without using templates. Read on and you will see why using this library is easier than using boost::any<> if your datatypes can be limited to primitives and string.
DynVal is a simple object that uses assignment and type casting operators to contain primitives and std::string. Using it is easy:
DynVal val = 1234; // type() == TINT32
val.as_s(); // to string
val = "1234"; // type() now TSTRING
val.as_i32(); // coerce to int32
(int32_t)val; // coerce using cast
C++ Applications that gather and report data in JSON format, or communicate with other processes often resort to map<string,string>. For large datasets, this can use up extra memory for the repeating keys, and CPU for all of the marshaling. DynMap is a map<const SPFieldDef,DynVal>, meaning the values can be any primitive type or string and the keys are declared once and shared. This has the following advantages:
- speed: pointer comparison rather than string comparison in map indexing
- memory: shared names, rather than multiple string copies
- names are defined once, no chance to misspell throughout code
- marshaling : Easier to use more efficient marshaling
The Normalize() function will take a DynMap object and convert the values to
match the types defined in the keys (SPFieldDef). Think of the FieldDefs as
the schema. This puts the conversion into a single step, and the application
can then use the DynMap values as the schema defines to marshal the data without
worrying about conversion each encountered value.
// app defines schema for fields
static const SPFieldDef NAME = FieldDef::alloc(TSTRING, "name");
static const SPFieldDef NUMBER = FieldDef::alloc(TUINT32, "number");
static const SPFieldDef ACTIVE = FieldDef::alloc(TUINT8, "active");
static const SPFieldDef UID = FieldDef::alloc(TINT64, "uid");
static const SPFieldDef HEIGHT = FieldDef::alloc(TINT32, "height");
void testfunc() {
DynMap obj;
obj[NAME] = "Kareem";
obj[NUMBER] = 33; // created as TINT32
obj[ACTIVE] = false; // created as TINT32
obj[UID] = 2348429; // created as TINT32
obj[HEIGHT] = "86"; // created as TSTRING
Dyno::Normalize(obj);
// types now match FieldDef
ASSERT_EQ(TUINT32, obj[NUMBER].type());
ASSERT_EQ(TUINT8, obj[ACTIVE].type());
ASSERT_EQ(TINT64, obj[UID].type());
ASSERT_EQ(TINT32, obj[HEIGHT].type());
}