State and Workflow Patterns

Feature Rollout Case

A rollout rule can decide which typed records receive a feature.

rollout predicate A predicate function keeps a feature gate separate from the loop that applies it.

Feature Rollout Case

regionFlag
rollout.ts
Replay: real traced execution (multi-file project)
type User = {
    id: number;
    region: "us" | "eu";
};

function enabledFor(user: User, regionFlag: "us" | "eu"): boolean {
    return user.region === regionFlag;
}

const regionFlag: "us" | "eu" = "us";
const users: User[] = [
    { id: 1, region: "us" },
    { id: 2, region: "eu" },
    { id: 3, region: "us" }
];

const enabled: number[] = [];
for (const user of users) {
    if (enabledFor(user, regionFlag)) {
        enabled.push(user.id);
    }
}

console.log(`enabled=${enabled.join(",")}`);

type User = {
    id: number;
    region: "us" | "eu";
};

function enabledFor(user: User, regionFlag: "us" | "eu"): boolean {
    return user.region === regionFlag;
}

const regionFlag: "us" | "eu" = "eu";
const users: User[] = [
    { id: 1, region: "us" },
    { id: 2, region: "eu" },
    { id: 3, region: "us" }
];

const enabled: number[] = [];
for (const user of users) {
    if (enabledFor(user, regionFlag)) {
        enabled.push(user.id);
    }
}

console.log(`enabled=${enabled.join(",")}`);

  1. regionFlag ← us, users ← [object Object],[object Object],[object Object]

    7    return user.region === regionFlag;8}910const regionFlag→ us: "us" | "eu" = "us";  //@regionFlag="eu"11const users→ [object Object],[object Object],[object Object]: User[] = [12    { id: 1, region: "us" },13    { id: 2, region: "eu" },14    { id: 3, region: "us" }15];1617const enabled→ (empty): number[] = [];18for (const user of users) {

  2. function enabledFor(user: User, regionFlag: "us" | "eu"): boolean

    pass 1 of 3
    3    region: "us" | "eu";4};56function enabledFor(user[object Object]: User, regionFlagus: "us" | "eu"): boolean {7    return user.region === regionFlagus;8}
    All 3 passes — pass 1 is the card above
    passenableduser.id
    1(empty)1
    2——
    313

  3. if (enabledFor(user, regionFlag))

    pass 1 of 2
    17const enabled: number[] = [];18for (const user of users) {19    if (enabledFor(user[object Object], regionFlagus)) {20        enabled.push(user.id1);21    }
    values this step(empty)enabled

  4. if (enabledFor(user, regionFlag))

    pass 2 of 2
    17const enabled: number[] = [];18for (const user of users) {19    if (enabledFor(user[object Object], regionFlagus)) {20        enabled.push(user.id3);21    }
    values this step1enabled

  5. console.log(`enabled=${enabled.join(",")}`);

    21    }22}2324console.log(`enabled=${enabled1,3.join(",")}`);
    outputenabled=1,3

  1. regionFlag ← eu, users ← [object Object],[object Object],[object Object]

    7    return user.region === regionFlag;8}910const regionFlag→ eu: "us" | "eu" = "eu";11const users→ [object Object],[object Object],[object Object]: User[] = [12    { id: 1, region: "us" },13    { id: 2, region: "eu" },14    { id: 3, region: "us" }15];1617const enabled→ (empty): number[] = [];18for (const user of users) {

  2. function enabledFor(user: User, regionFlag: "us" | "eu"): boolean

    pass 1 of 3
    3    region: "us" | "eu";4};56function enabledFor(user[object Object]: User, regionFlageu: "us" | "eu"): boolean {7    return user.region === regionFlageu;8}
    All 3 passes — pass 1 is the card above
    passenableduser.id
    1——
    2(empty)2
    3——

  3. if (enabledFor(user, regionFlag))

    17const enabled: number[] = [];18for (const user of users) {19    if (enabledFor(user[object Object], regionFlageu)) {20        enabled.push(user.id2);21    }
    values this step(empty)enabled

  4. console.log(`enabled=${enabled.join(",")}`);

    21    }22}2324console.log(`enabled=${enabled2.join(",")}`);
    outputenabled=2