Evaluating flags

The Variation method determines which variation of a flag LaunchDarkly serves to the current context. It requires the flag key and a fallback value. After the context is evaluated, you can view it on the Contexts list.

In the client-side .NET SDK, there is a variation method for each type, such as BoolVariation or StringVariation.

Here is an example:

client.BoolVariation("flag-key-123abc", false);
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The variation method determines which variation of a flag LaunchDarkly serves to the current context. It requires the flag key and a fallback value. After the context is evaluated, you can view it on the Contexts list. When LDClient is initialized for the first time at app launch, contexts receive the feature flag fallback values until an initial connection to LaunchDarkly completes.

In Android, there is a variation method for each type, such as boolVariation or stringVariation.

Here is an example:

boolean variationResult = client.boolVariation(flagKey, false);
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The variation methods determine which variation of a flag is served to the current context. The variation method signatures take the feature flag key and a fallback value. When the client is initialized for the first time, contexts receive the feature flag fallback values until an initial connection to LaunchDarkly completes.

There are variation methods for each type, such as BoolVariation or StringVariation.

Here is an example:

bool show_feature = client.BoolVariation("flag-key-123abc", false);
if (show_feature) {
    // Application code to show the feature
} else {
    // The code to run if the feature is off
}
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

To learn more, read the Client documentation.

The variation method determines which variation of a flag LaunchDarkly serves to a specific user. It requires the flag key and a fallback value. After the user is evaluated, you can view it on the Contexts list.

To evaluate any feature flag for the current user, call variation:

const flagValue = client.variation('flag-key-123abc', false);
// proceed based on flag value, for example:
if (flagValue)  {
  // feature flag targeting is on
} else {
  // feature flag targeting is off
}
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You must provide all relevant user attributes for each evaluation for your targeting rules to apply correctly.

The return value of variation is always either one of the variations you defined for your flag in the flag's Variations tab, or the fallback value. The fallback value is the second parameter to variation.

You can also fetch all flags for the current user.

Here is an example:

const flags = client.allFlags();
const flagValue = flags['flag-key-123abc'];
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This returns a key-value map of all your feature flags. It contains null values for any flags that could not be evaluated.

Both of these methods are synchronous. The client always has the last known flag values in memory, so retrieving them does not involve any input/output (I/O).

The variation methods determine which variation of a flag LaunchDarkly serves to the current context. variation calls take the feature flag key and a fallback value. After the context is evaluated, you can view it on the Contexts list. When the client is initialized for the first time at app launch, end users receive the feature flag fallback values until an initial connection to LaunchDarkly completes.

In Flutter, there is a variation method for each type, such as boolVariation or stringVariation.

Here is an example:

bool variationResult = client.boolVariation(flagKey, false);
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

To learn more, read boolVariation.

The variation functions determine which variation of a flag LaunchDarkly serves the current context. Variation functions take the feature flag key and a fallback value as parameters. After the context is evaluated, you can view it on the Contexts list. If the flag does not exist, cannot be cast to the correct return type, or the LDClient is not started, the function returns the fallback value.

In the iOS SDK, there is a variation method for each type, such as boolVariation or jsonVariation.

Here is an example:

let boolFlagValue = LDClient.get()!.boolVariation(forKey: "bool-flag-key-123abc", defaultValue: false)
let jsonFlagValue = LDClient.get()!.jsonVariation(forKey: "json-flag-key-456def", defaultValue: ["enabled": false, "special": "none"])
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The variation method determines which variation of a flag LaunchDarkly serves to the current context. variation calls take the feature flag key and a fallback value. After the context is evaluated, you can view it on the Contexts list.

Here is an example of the variation method:

client.variation('flag-key-123abc', false);
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The variation method determines which variation of a flag LaunchDarkly serves to the current context. It requires the flag key and a fallback value. After the context is evaluated, you can view it on the Contexts list.

Here is an example:

const value = client.variation('flag-key-123abc', false);
COPY

You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The variation method determines the flag variation to serve for a specific context.

In React Native, there is a variation method for each type, such as boolVariation or stringVariation. In the React Native SDK version 10, there is also a hook for each type, such as useBoolVariation or useStringVariation.

Variation calls take the feature flag key and a fallback value. When ReactNativeLDClient is initialized for the first time at app launch, end users receive feature flag fallback values until an initial connection to LaunchDarkly is completed. You are not required to specify a context when you initialize ReactNativeLDClient. If you do not specify a context initially, end users will also receive fallback values until you do specify a context by calling identify(). To learn more, read Identifying and changing contexts.

Here is an example:

const boolResult = useBoolVariation('bool-flag-key-123abc', false);
const numResult = useNumberVariation('numeric-flag-key-123abc', 2);
const stringResult = useStringVariation('string-flag-key-123abc', '');
const jsonResult = useJsonVariation('json-flag-key-123abc', {});
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

To learn more, read boolVariation.

The SDK also includes an untyped method to determine the variation of a feature flag. To learn more, read variation. We recommend using the strongly typed variation methods, such as boolVariation, which perform type checks and handle type errors.

The *variation methods determines which variation of a flag LaunchDarkly serves to the current context. The calls require the flag key and a fallback value. After the context is evaluated, you can view it on the Contexts list.

In the Roku SDK, there is a variation method for each type, such as boolVariation and intVariation.

Here is an example:

' typed variations
myInt = launchDarkly.intVariation("flag-key-123abc", 123)
myBool = launchDarkly.boolVariation("flag-key-123abc", false)
myString = launchDarkly.stringVariation("flag-key-123abc", "hello world!")
myObjectOrArray = launchDarkly.jsonVariation("flag-key-123abc", {"value": 123})
' generic variation
myValue = launchDarkly.variation("flag-key-123abc", false)
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The Variation methods determine which variation of a flag LaunchDarkly serves to a specific context. The methods require the flag key, the Context to evaluate, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

In .NET, there is a Variation method for each type:

• BoolVariation
• DoubleVariation
• FloatVariation
• IntVariation
• JsonVariation
• StringVariation.

Here is an example:

var value = client.BoolVariation("your.feature.key", context, false);
COPY

You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The variation methods determine which variation of a flag LaunchDarkly serves to a specific user. In Apex, there is a variation method for each type, such as boolVariation or stringVariation. The methods take an LDUser, a feature flag key, and a fallback value. After the user is evaluated, you can view it on the Contexts list.

Here is an example:

Boolean value = client.boolVariation(user, 'your.feature.key', false);
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You must provide all relevant user attributes for each evaluation for your targeting rules to apply correctly.

The variation family of functions determine which variation of a flag LaunchDarkly serves to a specific context. The functions require a context, feature flag key, and fallback value. After the context is evaluated, you can view it on the Contexts list.

In C++, there is a variation function for each type, such as BoolVariation or StringVariation.

Here is an example:

bool value = client.BoolVariation(context, "flag-key-123abc", false);
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The variation function determines which variation of a flag LaunchDarkly serves to a specific context. The functions take a flag key, context, fallback value, and an instance tag. In the example below, the fallback value is false. The instance tag is optional. After the context is evaluated, you can view it on the Contexts list.

Flag = ldclient:variation(<<"flag-key-123abc">>, #{key => <<"context-key-123abc">>,}, false, your_instance)
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The Variation methods determine which variation of a flag LaunchDarkly serves to a specific context. Variation methods take the feature flag key, a context, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

In Go, there is a Variation method for each type:

• BoolVariation
• IntVariation
• Float64Variation
• StringVariation
• JSONVariation, which can be any JSON type.

Here is an example:

result, _ := client.BoolVariation("your.feature.key", context, false)
// result is now true or false depending on the setting of this boolean feature flag
COPY

You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly. To learn more about constructing the context, read Context configuration.

If you are using OpenTelemetry, then instead of using the Variation method for each type, you must use the VariationCtx method for each type. For example, use BoolVariationCtx rather than BoolVariation. The methods are the same except that the VariationCtx methods also require a Go context parameter. This Go context is used in the hook implementation that provides OpenTelemetry support. To learn more, read OpenTelemetry.

The variation family of functions determine which variation of a flag LaunchDarkly serves to a specific context. The functions take a Client, Context, feature flag key, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

In Haskell, there is a variation function for each type:

• boolVariation
• intVariation
• doubleVariation
• stringVariation
• jsonVariation

Here is an example:

myBoolVariation <- boolVariation client "flag-key-123abc" context False
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly. To learn more about constructing the context, read Context configuration.

The variation methods determine which variation of a flag LaunchDarkly serves to a specific context. The variation methods take the feature flag key, an LDContext, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

In Java, there is a variation method for each type:

• boolVariation
• intVariation
• doubleVariation
• stringVariation
• jsonValueVariation, which can be of any JSON type.

Here is an example:

boolean value = client.boolVariation("flag-key-123abc", context, false);
COPY

You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly.

The variation family of functions determine which variation of a flag LaunchDarkly serves to a specific context. The functions take a context, feature flag key, and fallback value. After the context is evaluated, you can view it on the Contexts list.

In Lua, there is a variation function for each type, such as boolVariation or stringVariation.

Here is an example:

local value = client:boolVariation(context, "flag-key-123abc", false)
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You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly. To learn more, read boolVariation.

The variation method determines which variation of a flag LaunchDarkly serves to a specific context. variation calls take the feature flag key, an LDContext, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

Here is an example:

client.variation('flag-key-123abc', context, false,
  (err, value) => {
    // check value and proceed accordingly
  });
COPY

You must provide all relevant attributes for each evaluation for your targeting rules to apply correctly.

The variation method determines which variation of a flag LaunchDarkly serves to a specific context. variation calls take the feature flag key, an LDContext, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

Here is an example:

$value = $client->variation($key, $context, false);
COPY

You must provide all relevant attributes for each evaluation for your targeting rules to apply correctly.

The variation method determines which variation of a flag LaunchDarkly serves to a specific context. variation calls take the feature flag key, a Context, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

Here is an example:

show_feature = ldclient.get().variation("your.feature.key", context, False)
COPY

You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly. To learn more about constructing the context, read Context configuration.

The variation method determines which variation of a flag LaunchDarkly serves to a specific context. variation calls take the feature flag key, an LDContext or user hash, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

Here is an example:

value = client.variation("your.feature.key", context, false)
COPY

You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly. To learn more about constructing the context, read Context configuration.

The variation methods determine which variation of a flag LaunchDarkly serves to a specific context. variation methods take a Context, the feature flag key, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

In Rust, there is a variation method for each type:

• bool_variation,
• int_variation,
• float_variation,
• str_variation for strings, and
• json_variation, which can be any JSON type.

Here is an example:

let result = client.bool_variation(&context, "your.feature.key", false);
// result is now true or false depending on the setting of this boolean feature flag
COPY

You must provide all relevant context attributes for each evaluation for your targeting rules to apply correctly. To learn more about constructing the context, read Context configuration.

The variation method determines which variation of a feature flag a context receives. variation calls take the feature flag key, an LDContext, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

Here is an example:

const flagValue = await client.variation('flag-key-123abc', context, false);
COPY

You must provide all relevant attributes for each evaluation for your targeting rules to apply correctly.

To learn more, read variation. The LDClient also provides typed variation methods for type-safe usage in TypeScript: boolVariation, stringVariation, numberVariation, jsonVariation.

The variation method determines which variation of a feature flag a context receives. variation calls take the feature flag key, an LDContext, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

Here is an example:

const flagValue = await client.variation('flag-key-123abc', context, false);
COPY

You must provide all relevant attributes for each evaluation for your targeting rules to apply correctly.

To learn more, read variation. The LDClient also provides typed variation methods for type-safe usage in TypeScript: boolVariation, stringVariation, numberVariation, jsonVariation.

The variation method determines which variation of a feature flag a context receives. variation calls take the feature flag key, an LDContext, and a fallback value. After the context is evaluated, you can view it on the Contexts list.

Here is an example:

const flagValue = await client.variation('flag-key-123abc', context, false);
COPY

You must provide all relevant attributes for each evaluation for your targeting rules to apply correctly.

To learn more, read variation. The LDClient also provides typed variation methods for type-safe usage in TypeScript: boolVariation, stringVariation, numberVariation, jsonVariation.