Transfer practice · safeStock(item) returns zero for a missing record or absent quantity, and clamps a negative quantity to zero. It does not cap positive stock at one.

Repair an incomplete quest tracker: practice

v3 · Activity 1 of 1 · missing-data · guards · validation · 12 min Runs here

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Mini-mission

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Your task

safeStock(item) returns zero for a missing record or absent quantity, and clamps a negative quantity to zero. It does not cap positive stock at one.

Interface: progress(quest:{done:number?,total:number?}?) -> number

Input	Expected
Missing item`nil`	`0`
Negative stock`{ quantity = -3 }`	`0`
Positive stock`{ quantity = 14 }`	`14`

See another example

local function progress(quest)
    if quest == nil then return 0 end
    local total = quest.total or 0
    if total <= 0 then return 0 end
    local done = quest.done or 0
    return math.min(1, math.max(0, done / total))
end
return progress

The record guard precedes field access. The total guard prevents dividing by zero, then clamps the ratio.

Syntax in this activity

New syntax: /, guard clauses

Earlier ideas used here

nil
types
dictionaries
return-values
if-else

Explain more

Reading quest.done when quest is nil fails before a fallback on the field can help. Check the outer record first.

Define policies explicitly: a missing quest or nonpositive total gives 0 progress; missing done means 0. Valid progress is clamped from 0 to 1.

math.max and math.min select numeric limits. They do not replace type validation for arbitrary remote input; this activity supplies numeric fields or nil.

Explain this code

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

  progressquest
     quest     0 
     total  quest.total  0
     total  0   0 
     done  quest.done  0
     math.min1, math.max0, done  total

 progress

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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

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local function progress(quest)
    if quest == nil then return 0 end
    local total = quest.total or 0
    if total <= 0 then return 0 end
    local done = quest.done or 0
    return math.min(1, math.max(0, done / total))
end
return progress

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Experiment Output

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Code

Luau

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local function safeStock(item)
    return item.quantity
end
return safeStock

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

Your output will appear here.

Ready

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Your task

safeStock(item) returns zero for a missing record or absent quantity, and clamps a negative quantity to zero. It does not cap positive stock at one.

Interface: progress(quest:{done:number?,total:number?}?) -> number

Input	Expected
Missing item`nil`	`0`
Negative stock`{ quantity = -3 }`	`0`
Positive stock`{ quantity = 14 }`	`14`

See another example

local function progress(quest)
    if quest == nil then return 0 end
    local total = quest.total or 0
    if total <= 0 then return 0 end
    local done = quest.done or 0
    return math.min(1, math.max(0, done / total))
end
return progress

The record guard precedes field access. The total guard prevents dividing by zero, then clamps the ratio.

Syntax in this activity

New syntax: /, guard clauses

Earlier ideas used here

nil
types
dictionaries
return-values
if-else

Explain more

Reading quest.done when quest is nil fails before a fallback on the field can help. Check the outer record first.

Define policies explicitly: a missing quest or nonpositive total gives 0 progress; missing done means 0. Valid progress is clamped from 0 to 1.

math.max and math.min select numeric limits. They do not replace type validation for arbitrary remote input; this activity supplies numeric fields or nil.

Explain this code

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

  progressquest
     quest     0 
     total  quest.total  0
     total  0   0 
     done  quest.done  0
     math.min1, math.max0, done  total

 progress

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 progress(quest)
    if quest == nil then return 0 end
    local total = quest.total or 0
    if total <= 0 then return 0 end
    local done = quest.done or 0
    return math.min(1, math.max(0, done / total))
end
return progress

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

Experiment Output

Your output will appear here.