Transfer practice · labelOrFallback(value: unknown): string preserves a string, including empty text, and returns "Unnamed" for other types.

Describe and refine typed data: practice

v3 · Activity 1 of 1 · types · refinement · 12 min Runs here

Chapter outline

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Mini-mission

Use a familiar idea in a different task. Read the changed requirement before running.

Your task

labelOrFallback(value: unknown): string preserves a string, including empty text, and returns "Unnamed" for other types.

Interface: doubleNumber(value:unknown) -> number

Input	Expected
Text`"Lamp"`	`"Lamp"`
Empty text`""`	`""`
Number is not a label`5`	`"Unnamed"`

See another example

local function usableCount(value: unknown): number
    if type(value) == "number" then
        return math.max(0, value)
    end
    return 0
end
return usableCount

The type check makes the numeric operation meaningful. The fallback handles strings, booleans and nil.

Syntax in this activity

New syntax: : unknown, : number, type refinement

Earlier ideas used here

types
nil
functions
parameters
if-else

Explain more

Luau annotations such as value: number describe intended types for static analysis. They are not runtime permission checks and do not convert a string into a number.

A value typed unknown must be checked before you use it as a specific type. if type(value) == "number" then narrows it inside that branch.

This activity returns twice a numeric input and zero for other types. A standalone runtime compiles annotations, but this editor does not claim the full Roblox Studio type checker or autocomplete.

Explain this code

Select a word or symbol in this authored example. Your editor draft stays unchanged.

  doubleNumbervalue: unknown: number
     value  2

 doubleNumber

Choose a highlighted part to see what it means.

Free experiment

This is a private experiment copy. It does not replace your answer or complete the activity.

These inputs apply when your scratchpad returns the function described by the activity interface.

Test different inputs

Font size Plain text

local function usableCount(value: unknown): number
    if type(value) == "number" then
        return math.max(0, value)
    end
    return 0
end
return usableCount

Luau keyword highlighting · Ctrl/⌘ + Enter: Run · Esc: leave editorTab inserts indentation

Experiment Output

Your output will appear here.

Reset starter

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Code

Luau

Font size Plain text

local function labelOrFallback(value: unknown): string
    return tostring(value)
end
return labelOrFallback

Luau keyword highlighting · Ctrl/⌘ + Enter: Run · Esc: leave editorTab inserts indentation

Your output will appear here.

Ready

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Your task

labelOrFallback(value: unknown): string preserves a string, including empty text, and returns "Unnamed" for other types.

Interface: doubleNumber(value:unknown) -> number

Input	Expected
Text`"Lamp"`	`"Lamp"`
Empty text`""`	`""`
Number is not a label`5`	`"Unnamed"`

See another example

local function usableCount(value: unknown): number
    if type(value) == "number" then
        return math.max(0, value)
    end
    return 0
end
return usableCount

The type check makes the numeric operation meaningful. The fallback handles strings, booleans and nil.

Syntax in this activity

New syntax: : unknown, : number, type refinement

Earlier ideas used here

types
nil
functions
parameters
if-else

Explain more

Luau annotations such as value: number describe intended types for static analysis. They are not runtime permission checks and do not convert a string into a number.

A value typed unknown must be checked before you use it as a specific type. if type(value) == "number" then narrows it inside that branch.

This activity returns twice a numeric input and zero for other types. A standalone runtime compiles annotations, but this editor does not claim the full Roblox Studio type checker or autocomplete.

Explain this code

Select a word or symbol in this authored example. Your editor draft stays unchanged.

  doubleNumbervalue: unknown: number
     value  2

 doubleNumber

Choose a highlighted part to see what it means.

Free experiment

This is a private experiment copy. It does not replace your answer or complete the activity.

These inputs apply when your scratchpad returns the function described by the activity interface.

Test different inputs

Font size Plain text

local function usableCount(value: unknown): number
    if type(value) == "number" then
        return math.max(0, value)
    end
    return 0
end
return usableCount

Luau keyword highlighting · Ctrl/⌘ + Enter: Run · Esc: leave editorTab inserts indentation

Experiment Output

Your output will appear here.