Custom Types

DataStorm supports custom types for a topic’s Key, Value, and UpdateTag,
as well as for the key and sample filter criteria types.

All types used with DataStorm must support encoding to and decoding from a std::vector<byte>.

For types defined in Slice, DataStorm automatically uses the Slice encoding.

For built-in Slice types (e.g., string, int, float), no additional steps are required.
For custom Slice types, you must include the Slice-to-C++ generated code in your application.

Example: Built-in Slice Types

CPP

Topic<string, float> temperatures{node, "temperatures"};

In this example, DataStorm uses the Slice encoding for both string and float. No additional code or configuration is needed because both string and float are Slice built-in types.

Example: Custom Slice Type

If you define a custom type in Slice, such as:

SLICE

module ClearSky
{
    class AtmosphericConditions
    {
        /// The temperature in degrees Celsius.
        double temperature;

        /// The humidity in percent.
        double humidity;
    }
}

You must include the slice2cpp-generated code when building your application.

DataStorm will use the Slice encoding for both parameters:

string is encoded as a built-in Slice type.
ClearSky::AtmosphericConditions is encoded and decoded using the generated Slice code.

CPP

Topic<string, ClearSky::AtmosphericConditionsPtr> temperatures{node, "temperatures"};

Example: Non-Slice Types

If your types are not defined in Slice, you must provide specializations of the DataStorm::Encoder and DataStorm::Decoder templates for those types.

Additional Requirements

For partial updates, DataStorm needs to clone values. By default, DataStorm performs cloning using the type’s copy constructor.

In some cases, using the copy constructor may not be appropriate — for example, when the value is a std::shared_ptr or another reference type that should not be deep-copied.

The DataStorm::Cloner template allows applications to customize how values are cloned for their own types. You can specialize this template to define a custom clone behavior that suits your data types.

Stringification

DataStorm converts types to strings using the operator<< overload for std::ostream in two scenarios:

Tracing
DataStorm traces include the string representation of keys. If a key type does not support string conversion via operator<<, DataStorm falls back to printing the key’s typeid and memory address.
Regex Filters
DataStorm provides a built-in _regex filter. The regular expression is applied to the string representation of the key or value, which requires that the type implement a valid operator<< overload.