Sum an Array: Total Boost Score

Accumulate over an array to compute totals like collected boosts.

📖 Reference & full walkthrough: Sum an Array: Total Boost Score

🧩 Your capstone piece: Total-boosts and total-time aggregation

Overview

An array in Verse is a fixed-order container of same-typed values: []int, []float, []agent, etc. Summing an array is the gateway skill for almost every score system, leaderboard, damage calculator, or resource counter you will ever build in UEFN.

The pattern is always the same:

1. Declare a var Total : int = 0 (or float).
2. for (Value : MyArray) — iterate every element.
3. set Total += Value — accumulate.
4. Use Total however you like: display it, compare it, award XP with it.

In this article the "however you like" part is a hud_message_device that flashes the gold total on every player's screen, triggered by the last pressure plate on a cel-shaded pirate ship docked in a sunny lagoon.

API Reference

trigger_device

Used to relay events to other linked devices.

Full public surface, resolved verbatim from the live Epic digest (Fortnite.digest.verse). Inherited members are merged from trigger_base_device.

trigger_device<public> := class<concrete><final>(trigger_base_device):

Events (subscribe a handler to react):

Methods (call these to make the device act):

team

Full public surface, resolved verbatim from the live Epic digest (Verse.digest.verse).

team<native><public> := class<unique><epic_internal>:

hud_message_device

Used to show custom HUD messages to one or more agents.

Full public surface, resolved verbatim from the live Epic digest (Fortnite.digest.verse).

hud_message_device<public> := class<concrete><final>(creative_device_base):

Events (subscribe a handler to react):

Methods (call these to make the device act):

Walkthrough

The scenario

Five pressure plates are hidden under treasure chests along the ship's deck. Stepping on each plate adds that chest's gold value to a running tally. The fifth plate fires a trigger_device that calls our Verse device, which sums the array and shows the grand total via hud_message_device.

using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }
using { /Verse.org/Native }

# Localisation helper — message params must be `message`, not raw string.
TreasureMessage<localizes>(S : string) : message = "{S}"

treasure_tally_device := class(creative_device):

    # ── Editable device references ────────────────────────────────────────────
    # Wire this to the trigger_device that fires when the last chest is opened.
    @editable
    FinalChestTrigger : trigger_device = trigger_device{}

    # HUD message device set to "All Players" in its properties.
    @editable
    ScoreHUD : hud_message_device = hud_message_device{}

    # ── Gold values for each of the five treasure chests ─────────────────────
    # Edit these in the Details panel or hard-code them here.
    # Index 0 = bow chest, 1 = port side, 2 = starboard, 3 = crow's nest, 4 = captain's cabin.
    @editable
    ChestGoldValues : []int = array{50, 120, 75, 200, 350}

    # ── Lifecycle ─────────────────────────────────────────────────────────────
    OnBegin<override>()<suspends> : void =
        # Subscribe: when the final chest trigger fires, run OnFinalChestTriggered.
        FinalChestTrigger.TriggeredEvent.Subscribe(OnFinalChestTriggered)

        # Give the HUD message device a persistent display time so the
        # score stays on screen until we explicitly hide it.
        ScoreHUD.SetDisplayTime(0.0)

    # ── Event handler ─────────────────────────────────────────────────────────
    # TriggeredEvent sends ?agent, so the handler receives ?agent.
    OnFinalChestTriggered(MaybeAgent : ?agent) : void =
        # 1. Sum the chest gold values.
        var TotalGold : int = 0
        for (GoldValue : ChestGoldValues):
            set TotalGold += GoldValue

        # 2. Build the display string and push it to the HUD.
        #    Show() with no agent arg broadcasts to ALL players.
        ScoreHUD.Show(TreasureMessage("Treasure Haul: {TotalGold} Gold!"))

        # 3. If a real agent triggered the plate, also show them a personal
        #    confirmation using the agent-specific overload of Show.
        if (A := MaybeAgent?):
            ScoreHUD.Show(A, TreasureMessage("You found it all! {TotalGold} Gold!"))

Line-by-line explanation

Common patterns

Pattern 1 — Summing floats (damage dealt across a round)

The same loop works for []float. Here a trigger fires at round end and the device sums each player's damage log.

using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }
using { /Verse.org/Native }

DamageMessage<localizes>(S : string) : message = "{S}"

damage_summary_device := class(creative_device):

    @editable
    RoundEndTrigger : trigger_device = trigger_device{}

    @editable
    DamageHUD : hud_message_device = hud_message_device{}

    # Damage dealt by each player this round (populated elsewhere in your project).
    @editable
    DamageLog : []float = array{340.5, 210.0, 512.75, 88.25}

    OnBegin<override>()<suspends> : void =
        RoundEndTrigger.TriggeredEvent.Subscribe(OnRoundEnd)
        DamageHUD.SetDisplayTime(5.0)   # Show for 5 seconds then auto-hide.

    OnRoundEnd(MaybeAgent : ?agent) : void =
        var TotalDamage : float = 0.0
        for (D : DamageLog):
            set TotalDamage += D
        # Truncate to int for a cleaner display.
        TotalInt : int = Int[TotalDamage]  # failable cast — use in if
        if (T := Int[TotalDamage]):
            DamageHUD.Show(DamageMessage("Team Damage: {T}"))
        else:
            DamageHUD.Show(DamageMessage("Team Damage: (overflow)"))

Pattern 2 — Conditional sum (only count chests the player actually opened)

Use an if inside the for loop to filter which elements contribute to the total. Here only chests worth more than 100 gold count as "legendary" and are summed separately. The trigger is also reconfigured at runtime with SetMaxTriggerCount.

using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }
using { /Verse.org/Native }

LegendaryMsg<localizes>(S : string) : message = "{S}"

legendary_tally_device := class(creative_device):

    @editable
    BonusTrigger : trigger_device = trigger_device{}

    @editable
    BonusHUD : hud_message_device = hud_message_device{}

    @editable
    AllChestValues : []int = array{50, 120, 75, 200, 350, 30, 500}

    OnBegin<override>()<suspends> : void =
        # Allow this bonus trigger to fire only once per match.
        BonusTrigger.SetMaxTriggerCount(1)
        BonusTrigger.TriggeredEvent.Subscribe(OnBonusTriggered)

    OnBonusTriggered(MaybeAgent : ?agent) : void =
        # Sum ONLY legendary chests (value > 100).
        var LegendaryTotal : int = 0
        var LegendaryCount : int = 0
        for (Value : AllChestValues, Value > 100):
            set LegendaryTotal += Value
            set LegendaryCount += 1

        BonusHUD.Show(LegendaryMsg("Legendary Chests: {LegendaryCount} | Gold: {LegendaryTotal}"))

        # Disable the trigger so it can never fire again (belt-and-suspenders).
        BonusTrigger.Disable()

Pattern 3 — Displaying a live running total as each chest is found

Each chest has its own trigger_device. Every trigger fires OnChestFound, which appends the chest's value to a mutable array and immediately updates the HUD. This uses GetTriggerCountRemaining to know how many chests are left.

using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }
using { /Verse.org/Native }

RunningMsg<localizes>(S : string) : message = "{S}"

running_tally_device := class(creative_device):

    # One trigger per chest — wire all five in the Details panel.
    @editable
    Chest1Trigger : trigger_device = trigger_device{}
    @editable
    Chest2Trigger : trigger_device = trigger_device{}
    @editable
    Chest3Trigger : trigger_device = trigger_device{}

    @editable
    LiveHUD : hud_message_device = hud_message_device{}

    # Gold value for each chest, parallel to the triggers above.
    @editable
    GoldValues : []int = array{50, 120, 350}

    # Accumulate found gold at runtime.
    var CollectedGold : []int = array{}

    OnBegin<override>()<suspends> : void =
        LiveHUD.SetDisplayTime(0.0)   # Persistent display.
        Chest1Trigger.TriggeredEvent.Subscribe(OnChest1Found)
        Chest2Trigger.TriggeredEvent.Subscribe(OnChest2Found)
        Chest3Trigger.TriggeredEvent.Subscribe(OnChest3Found)

    # Helper: append a value, recompute sum, refresh HUD.
    AddAndRefresh(GoldIndex : int) : void =
        if (Value := GoldValues[GoldIndex]):
            set CollectedGold = CollectedGold + array{Value}
        var Total : int = 0
        for (G : CollectedGold):
            set Total += G
        Remaining : int = Chest1Trigger.GetTriggerCountRemaining()
        LiveHUD.Show(RunningMsg("Gold so far: {Total}"))

    OnChest1Found(MaybeAgent : ?agent) : void = AddAndRefresh(0)
    OnChest2Found(MaybeAgent : ?agent) : void = AddAndRefresh(1)
    OnChest3Found(MaybeAgent : ?agent) : void = AddAndRefresh(2)

Gotchas

1. message is NOT a string

hud_message_device.Show() and SetText() both require a message, not a plain string. Always declare a <localizes> helper:

MyMsg<localizes>(S : string) : message = "{S}"

There is no StringToMessage function — the <localizes> function is the only bridge.

2. int and float do not auto-convert

If your chest values are []float but you want to display a rounded integer, use the failable Int[] cast inside an if:

if (T := Int[TotalFloat]):
    HUD.Show(MyMsg("{T}"))

Do not write TotalFloat + 0 hoping it becomes an int — the compiler will reject it.

3. TriggeredEvent sends ?agent, not agent

The handler signature must be (MaybeAgent : ?agent). Forgetting the ? causes a type mismatch compile error. Always unwrap before using:

if (A := MaybeAgent?):
    HUD.Show(A, MyMsg("Personal message"))

4. @editable arrays are set at edit time, not runtime

You cannot array.Add() to an @editable array — arrays in Verse are immutable by default. Use a separate var field (e.g. var CollectedGold : []int = array{}) and reassign with concatenation (set CollectedGold = CollectedGold + array{NewValue}).

5. SetMaxTriggerCount clamps to [0, 20]

Passing a value outside that range silently clamps it. 0 means unlimited — not zero triggers. If you want a one-shot trigger, pass 1.

6. Empty array sum is zero — that's fine

A for loop over an empty array simply never executes, leaving Total at its initial value. This is safe and expected behaviour, not a bug.