Types and Data Structures

Overview

This document outlines some of the common types and data structures defined by OpenFeature and referenced elsewhere in this specification.

Boolean

A logical true or false, as represented idiomatically in the implementation languages.

String

A UTF-8 encoded string.

Number

A numeric value of unspecified type or size. Implementation languages may further differentiate between integers, floating point numbers, and other specific numeric types and provide functionality as idioms dictate.

Structure

Structured data, presented however is idiomatic in the implementation language, such as JSON or YAML.

Datetime

A language primitive for representing a date and time, optionally including timezone information. If no timezone is specified, the date and time will be treated as UTC.

Evaluation Details

A structure representing the result of the flag evaluation process, and made available in the detailed flag resolution functions, containing the following fields:

• flag key (string, required)
• value (boolean | string | number | structure, required)
• error code (error code, optional)
• error message (string, optional)
• reason (string, optional)
• variant (string, optional)
• flag metadata (flag metadata)

Note

Some type systems feature useful constraints that can enhance the ergonomics of the evaluation details structure. For example, in the case of an unsuccessful evaluation, error code, reason, and error message will be set, and variant will not. If the type system of the implementation supports the expression of such constraints, consider defining them.

Resolution Details

A structure which contains a subset of the fields defined in the evaluation details, representing the result of the provider's flag resolution process, including:

• value (boolean | string | number | structure, required)
• error code (error code, optional)
• error message (string, optional)
• reason (string, optional)
• variant (string, optional)
• flag metadata (flag metadata, optional)

A set of pre-defined reasons is enumerated below:

Reason	Explanation
STATIC	The resolved value is static (no dynamic evaluation).
DEFAULT	The resolved value fell back to a pre-configured value (no dynamic evaluation occurred or dynamic evaluation yielded no result).
TARGETING_MATCH	The resolved value was the result of a dynamic evaluation, such as a rule or specific user-targeting.
SPLIT	The resolved value was the result of pseudorandom assignment.
CACHED	The resolved value was retrieved from cache.
DISABLED	The resolved value was the result of the flag being disabled in the management system.
UNKNOWN	The reason for the resolved value could not be determined.
STALE	The resolved value is non-authoritative or possibly out of date
ERROR	The resolved value was the result of an error.

Note

The reason should not be limited to the reasons enumerated above. It can be any of the pre-defined reasons, or any string value. Some type systems have features which can increase the ergonomics of reason, for instance a union of pre-defined types with a string, or a rust-style enumeration which allows for enumerated values to have associated content.

enum Reason {
    Static,
    Default,
    TargetingMatch,
    Split,
    Cached,
    Unknown,
    Stale,
    Error,
    Other(String)
}

let myReason = Reason::Other("my-reason".to_string());

Note

The resolution details structure is not exposed to the Application Author. It defines the data which Provider Authors must return when resolving the value of flags.

Error Code

An enumerated error code represented idiomatically in the implementation language.

Error Code	Explanation
PROVIDER_NOT_READY	The value was resolved before the provider was initialized.
FLAG_NOT_FOUND	The flag could not be found.
PARSE_ERROR	An error was encountered parsing data, such as a flag configuration.
TYPE_MISMATCH	The type of the flag value does not match the expected type.
TARGETING_KEY_MISSING	The provider requires a targeting key and one was not provided in the evaluation context.
INVALID_CONTEXT	The evaluation context does not meet provider requirements.
PROVIDER_FATAL	The provider has entered an irrecoverable error state.
GENERAL	The error was for a reason not enumerated above.

Evaluation Context

See evaluation context.

Evaluation Options

A structure containing the following fields:

• hooks (one or more hooks, optional)
• hook hints (hook hints structure, optional)

Flag Metadata

A structure which supports definition of arbitrary properties, with keys of type string, and values of type boolean, string, or number.

This structure is populated by a provider for use by an Application Author via the Evaluation API or an Application Integrator via hooks.

Provider Status

An enumeration of possible provider states.

Status	Explanation
NOT_READY	The provider has not been initialized.
READY	The provider has been initialized, and is able to reliably resolve flag values.
ERROR	The provider is initialized but is not able to reliably resolve flag values.
STALE	The provider's cached state is no longer valid and may not be up-to-date with the source of truth.
FATAL	The provider has entered an irrecoverable error state.
RECONCILING*	The provider is reconciling its state with a context change.

* static context (client-side) paradigm only

Provider Event Details

A structure defining a provider event payload, including:

• flags changed (string[], optional)
• message (string, optional)
• error code (error code, optional)
• event metadata (event metadata)

Event Details

A structure defining an event payload, including:

• provider name (string, required)
• flags changed (string[], optional)
• message (string, optional)
• error code (error code, optional)
• event metadata (event metadata)

Event Metadata

A structure supporting the addition of arbitrary event data. It supports definition of arbitrary properties, with keys of type string, and values of type boolean, string, or number.

Provider Events

An enumeration of provider events.

Event	Explanation
PROVIDER_READY	The provider is ready to perform flag evaluations.
PROVIDER_ERROR	The provider signaled an error.
PROVIDER_CONFIGURATION_CHANGED	A change was made to the backend flag configuration.
PROVIDER_STALE	The provider's cached state is no longer valid and may not be up-to-date with the source of truth.
PROVIDER_RECONCILING*	The context associated with the provider has changed, and the provider has not yet reconciled its associated state.
PROVIDER_CONTEXT_CHANGED*	The context associated with the provider has changed, and the provider has reconciled its associated state.

* static context (client-side) paradigm only

Handler Functions

A function or method which can be associated with a provider event, and runs when that event occurs. It declares an event details parameter.

Tracking Event Details

A structure which supports definition of arbitrary properties, including nested objects, similar to the evaluation context and object-typed flag values.

See tracking event details, evaluation context.