17. A system for dynamically generating classes and methods in memory comprising: a host programming language that transmits or receives instance data from an application programming interface; one or more computing devices; and one or more non-transitory storage devices storing instructions that, when executed by the one or more computing devices, cause the one or more computing devices to: receive a schema, which describes the format and properties of an instance object to be transmitted or received; convert, using a client library, raw schema data into an intermediate hierarchical data structure, an upper level of the hierarchical data structure including the properties of the instance object, and each property including data representing attributes of that property; dynamically at runtime generate parser classes for deserialization and methods from properties and attributes described in the intermediate hierarchical data structure based on the schema, wherein generating the parser classes comprises: iterating over each property defined in the schema and in any other schema referenced in the schema, and defining a new class for each non-scalar, non-array property defined by the schema; and store the generated parser classes and methods in memory, wherein the host programming language transmits or receives instance data to or from the application programming interface using the generated parser classes and methods.
17. A system for dynamically generating classes and methods in memory comprising: a host programming language that transmits or receives instance data from an application programming interface; one or more computing devices; and one or more non-transitory storage devices storing instructions that, when executed by the one or more computing devices, cause the one or more computing devices to: receive a schema, which describes the format and properties of an instance object to be transmitted or received; convert, using a client library, raw schema data into an intermediate hierarchical data structure, an upper level of the hierarchical data structure including the properties of the instance object, and each property including data representing attributes of that property; dynamically at runtime generate parser classes for deserialization and methods from properties and attributes described in the intermediate hierarchical data structure based on the schema, wherein generating the parser classes comprises: iterating over each property defined in the schema and in any other schema referenced in the schema, and defining a new class for each non-scalar, non-array property defined by the schema; and store the generated parser classes and methods in memory, wherein the host programming language transmits or receives instance data to or from the application programming interface using the generated parser classes and methods. 24. The system of claim 17 , wherein dynamically generating parser classes and methods comprises: for each union type, matching the property to defined types in an order that the defined types are listed in the schema; and responsive to a match, using a matching defined type to create a class property.