Tech/LxEngine/lxvar

From Athile

The lxvar class is intended as a simple, convenient class for dealing with arbitrary JSON-like data with reasonable efficiency. In addition to supporting the majority of standard Javascript 'var' functionality, the class also supports various features to aid in intermixing with native C++ types as well as persisting, validating, and responding to value changes.

Example Usage

Primitive types

Support for basic types: bool, int, float, double, and std::string.

lxvar v;        // default value is "undefined"
 
// Can store the following basic types
v = true;
v = 1;
v = 1.0f;
v = 1.0;
v = "one";
 
// Explicit conversion
bool b = v.as<bool>();
int i = v.as<int>();
float f = v.as<float>();
std::string s = v.as<std::string>();
 
// Implicit type conversion
int i = v;            // same as v.as<int>()
float f = v;          // same as v.as<float>()

¹ Implicit conversion is usually frowned upon as a C++ coding technique, as it "hides" what is happening from the reader; however, for a convenience class like lxvar, implicit conversions were deemed a good fit.

Arrays, Maps

to be completed

Map Specializations

In addition to a standard map implementation, other specialized map implementations are available. These provide the same map interface but also provide additional functionality:

• lxvar::orderedmap()
• lxvar::decoratedmap()

orderedmap

The orderermap implementation behaves like a standard map with one exception: the iteration order is equivalent to the insertion order of the keys. If a value is overwritten for a key, the key retains its original order.

The ordermap requires slightly more memory and is slightly less efficient than a standard map.

decoratedmap

to be completed

Objects

The wrap and unwrap2 functions can be used to store native C++ types in an lxvar.

lxvar data;
data["position"] = lxvar::wrap(glgeom::point3f(1, 2, 3));
 
auto& position = data["position"].unwrap2<glgeom::point3f>();

Interface

Class

Functions

query( string path ) -> lxvar

Searches the lxvar for a given property (using JSON syntax) and returns the value of that property. If that property, or any part of the property path, does not exist, then undefined is returned.

• Using this method alone, there is no way to distinguish between a property that exists and is set to undefined and a property that does not exist and thus returns undefined.

query( string path, type default_value ) -> lxvar

The same as the alternate version of query but returns the provided default if the property does not exist or is of an incompatible type.

Issues