A/B experiments

GetExperiment evaluates an experiment for a user and returns an ExperimentResult describing whether they were enrolled, which group they landed in, and the group's params.

ExperimentResult

type ExperimentResult struct {
    InExperiment bool   // enrolled in (not held out / allocated into) the experiment
    Group        string // the assigned group name (e.g. "control", "treatment")
    Params       any    // the group's params, or your defaultParams when not enrolled
}

Evaluating an experiment

c := shipeasy.NewClient(acct)            // bind the user once

// defaultParams is returned in r.Params when the user is NOT enrolled
// (held out, outside allocation, or the experiment isn't running).
r := c.GetExperiment("checkout_button", map[string]any{"color": "blue"})

if r.InExperiment {
    p := r.Params.(map[string]any)
    renderButton(p["color"])
} else {
    renderButton("blue") // control / default
}

When the user is not enrolled, Group is "control" and Params falls back to the defaultParams you passed.

Tracking conversions with Client.Track

To measure an experiment you log a conversion event. You already have a bound Client (the same one you called GetExperiment on), so call Track on it — the unit id is derived from the bound attribute map (user_id, else anonymous_id), so there's no user argument. The event is fire-and-forget POSTed to /collect:

c := shipeasy.NewClient(acct)
// ... present the treatment from c.GetExperiment(...) ...
c.Track("{{SUCCESS_EVENT}}", map[string]any{"amount": 49})

Client.Track(event, props) takes the event name and an optional property bag. This makes an experiment end-to-end Client-only: NewClient(user) → GetExperiment → Track. Track is fire-and-forget (never blocks your response) and a no-op under ConfigureForTesting / ConfigureForOffline.

Manual exposure

The server is stateless and never auto-logs an exposure. When you actually present the treatment, call LogExposure on the bound Client — the experiment is re-evaluated against the bound attributes (so bucketBy / anonymous traffic resolve correctly) and one exposure is logged if the user is enrolled:

c := shipeasy.NewClient(acct)
c.LogExposure("checkout_button")

See Advanced for bucketBy and sticky bucketing.