Assignments

Assignments are the mechanism through which a given Subject is assigned to a variation for a feature flag, experiment, or bandit.

Currently, the Eppo SDK supports the following assignment types:

• Boolean
• Integer
• Numeric
• JSON
• String

The SDK will return different results based on whether the subject details match the assignment rules you set in the Eppo UI.

Boolean Assignments

Boolean flags support simple on/off toggles. They're useful for simple, binary feature switches like blue/green deployments or enabling/disabling a new feature.

final variant = Eppo.getBooleanAssignment(
  'flag-key-123',
  false  // default value
);

// Use the variant value to determine which component to render
if (variant) {
  return renderFeatureEnabledComponent();
} else {
  return renderFeatureDisabledComponent();
}

String Assignments

String assignment return a string value that is set as the variation for the experiment. String flags are the most common type of flags for A/B/n tests and advanced targeting use cases.

final variant = Eppo.getStringAssignment(
  'flag-key-123',
  'version-a'  // default value
);

// Use the variant value to determine which component to render
switch(variant) {
  case 'version-a':
    return handleVersionA();
  case 'version-b':
    return handleVersionB();
  default:
    return handleDefaultVersion();
}

JSON Assignments

JSON flags work best for advanced configuration use cases. The JSON flag can include structured information such as:

• The text of marketing copy for a promotional campaign
• The address of a different hero image

Using this pattern, a team can make minor changes to the copy and design of a website without having to go through an entire code release process.

final defaultAssignment = {
  'hero': false,
  'heroImage': 'placeholder.png',
  'heroTitle': 'Placeholder Hero Title',
  'heroDescription': 'Placeholder Hero Description'
};

final campaignJson = Eppo.getJSONAssignment(
  'flag-key-123',
  defaultAssignment
);

if (campaignJson != null) {
  campaign.hero = true;
  campaign.heroImage = campaignJson['heroImage'] as String?;
  campaign.heroTitle = campaignJson['heroTitle'] as String? ?? '';
  campaign.heroDescription = campaignJson['heroDescription'] as String? ?? '';
}

// Use the campaign settings in your component
renderHero(campaign.heroImage, campaign.heroTitle, campaign.heroDescription);

Integer and Numeric Assignments

Integer and numeric assignments work the same way but return either an integer or a floating point number. These assignments are useful where you want to use a numeric value to drive business logic such as pricing on an item or a number of items to display in a list.

// Example of getting an integer assignment
final numberOfItems = Eppo.getIntegerAssignment(
  'flag-key-123',
  0  // default value
);

// Example of getting a numeric assignment
final price = Eppo.getNumericAssignment(
  'flag-key-123',
  0.0  // default value
);

// Use the assignments to drive business logic
renderItemList(numberOfItems);
renderPrice(price);

Assignment Logger Schema

The SDK will invoke the logAssignment method with an AssignmentEvent object containing the following fields:

class AssignmentEvent {
  /// The allocation the subject was assigned to
  final String? allocation;

  /// The experiment identifier
  final String? experiment;

  /// The feature flag identifier
  final String featureFlag;

  /// The format of the assignment
  final String format;

  /// The variation key that was assigned
  final String? variation;

  /// The subject identifier
  final String subject;

  /// The timestamp of the assignment
  final String timestamp;

  /// The subject attributes
  final Map<String, dynamic>? subjectAttributes;

  /// Additional metadata
  final Map<String, dynamic>? metaData;

  /// Details about the evaluation
  final Map<String, dynamic>? evaluationDetails;

Logging data to your data warehouse

Eppo's unique architecture makes it so Eppo never has to store your data. This means that you can use the assignment logging functions to send data to any data warehouse or logging system you want.

All you need to do is to provide a callback to the assignmentLogger parameter of the EppoConfig constructor.

/// Interface for logging assignment events
abstract class AssignmentLogger {
  /// Logs an assignment event
  void logAssignment(AssignmentEvent event);
}

// Initialize with custom configuration and wait for the client to be ready
await Eppo.initialize(
  PrecomputeArguments(subject: subject),
  SdkOptions(
    sdkKey: 'your-sdk-key',
    assignmentLogger: YourAssignmentLogger(),
  )
);

note

More details about logging and examples (with Segment, Rudderstack, mParticle, and Snowplow) can be found in the assignment logging page.