asserts.mdc

---
description: Roblox Luau Asserts module API reference for runtime type validation
alwaysApply: false
---
# Asserts Module

Runtime type validation for Luau. Located at `ReplicatedStorage.UserGenerated.Lang.Asserts`.

## Basic Usage

```luau

-- Direct validation (throws on failure)
local n = Asserts.Integer(someValue)
local s = Asserts.String(input)

-- Composed validators return functions
local validatePositiveInt = Asserts.IntegerPositive
local value = validatePositiveInt(input)
```

## Primitives

| Function | Description |
|----------|-------------|
| `Number(x)` | Any number |
| `String(x)` | UTF-8 validated string |
| `RawString(x)` | String without UTF-8 validation |
| `Boolean(x)` | Boolean value |
| `Buffer(x)` | Buffer type |
| `Function(x)` | Function type |
| `Thread(x)` | Coroutine thread |
| `Any(x)` | Passthrough, no validation |

## Numbers

| Function | Description |
|----------|-------------|
| `Finite(x)` | Excludes NaN and infinity |
| `FinitePositive(x)` | Finite and > 0 |
| `FiniteNonNegative(x)` | Finite and >= 0 |
| `Positive(x)` | > 0 (excludes NaN) |
| `NonNegative(x)` | >= 0 (excludes NaN) |
| `Real(x)` | Excludes NaN only |
| `Integer(x)` | Whole number, finite |
| `IntegerPositive(x)` | Integer >= 1 |
| `IntegerNonNegative(x)` | Integer >= 0 |
| `Index(x)` | Alias for IntegerPositive |
| `Unsigned32(x)` | 32-bit unsigned integer (direct validator) |
| `UInt32` | Returns a validator for 32-bit unsigned integers (factory) |
| `Range(a, b)` | Returns validator for [a, b] |
| `IntegerRange(a, b)` | Returns validator for integer [a, b] |

## Strings

| Function | Description |
|----------|-------------|
| `ASCII(x)` | Printable ASCII only (32-126) |
| `ASCIIRange(a, b)` | ASCII with length in [a, b] |
| `StringRange(a, b)` | UTF-8 with char count in [a, b] |
| `Pattern(pattern)` | Returns validator matching Lua pattern |
| `HexLower(x)` | Lowercase hex string |
| `HexUpper(x)` | Uppercase hex string |
| `Base64(x)` | Valid Base64 encoding |
| `UUID(x)` | UUID with dashes (36 chars) |
| `UUIDStripped(x)` | UUID without dashes (32 chars) |
| `IsoDate(x)` | ISO 8601 date string |

## Roblox Types

| Function | Description |
|----------|-------------|
| `Vector2(x)`, `Vector3(x)` | Basic vector validation |
| `Vector2Finite(x)`, `Vector3Finite(x)` | Vectors with finite components |
| `Vector2Unit(x)`, `Vector3Unit(x)` | Unit vectors (magnitude ≈ 1) |
| `Vector3Positive(x)` | All components > 0 |
| `CFrame(x)`, `CFrameFinite(x)` | CFrame validation |
| `UDim(x)`, `UDim2(x)`, `Rect(x)` | UI types |
| `Region3(x)`, `Region3int16(x)` | Region types |
| `Vector2int16(x)`, `Vector3int16(x)` | Integer vector types |
| `PhysicalProperties(x)` | PhysicalProperties validation |

## Instances

| Function | Description |
|----------|-------------|
| `Instance(x)` | Any Instance |
| `InstanceOf<T>(className)` | Returns validator using IsA |
| `InstanceClass<T>(className)` | Returns validator for exact ClassName |
| `Player(x)`, `Model(x)`, `Humanoid(x)` | Specific instance types |
| `BasePart(x)`, `Part(x)`, `MeshPart(x)` | Part types |
| `Sound(x)`, `Animation(x)`, `ParticleEmitter(x)` | Other common types |

## Enums

```luau
-- Validate EnumItem of specific type
local validateMaterial = Asserts.Enum(Enum.Material)
local mat = validateMaterial(Enum.Material.Plastic)

-- Validate enum by numeric value
local validateMaterialValue = Asserts.EnumValue(Enum.Material)
local matValue = validateMaterialValue(256)
```

## Collections

### Arrays

```luau
-- Validate array elements
local validateNumbers = Asserts.Array(Asserts.Integer)
local nums = validateNumbers({1, 2, 3})

-- Array with unique elements
local validateUniqueStrings = Asserts.UniqueArray(Asserts.String)

-- Transform elements (Coerce variants)
local toIntegers = Asserts.ArrayCoerce(Asserts.ToNumber(Asserts.Integer))
local nums = toIntegers({"1", "2", "3"}) -- {1, 2, 3}

-- Unique array with coercion
local toUniqueInts = Asserts.UniqueArrayCoerce(Asserts.ToNumber(Asserts.Integer))
```

### Maps

```luau
-- Validate key-value pairs
local validateScores = Asserts.Map(Asserts.String, Asserts.Integer)
local scores = validateScores({alice = 100, bob = 200})

-- Optional length limit
local limitedMap = Asserts.Map(Asserts.String, Asserts.Any, 10)

-- Map with key/value coercion
local coercedMap = Asserts.MapCoerce(Asserts.String, Asserts.ToNumber(Asserts.Integer))
```

### Tables (Structured Objects)

```luau
-- Validate specific keys (strict - no extra keys allowed)
local validatePlayer = Asserts.Table({
    name = Asserts.String,
    score = Asserts.IntegerNonNegative,
    active = Asserts.Boolean,
})

-- Permissive variant (ignores extra keys)
local validatePartial = Asserts.TablePermissive({
    id = Asserts.String,
})

-- Transform values (Coerce variant)
local parseConfig = Asserts.TableCoerce({
    port = Asserts.ToNumber(Asserts.IntegerPositive),
    host = Asserts.String,
})
```

## Combinators

```luau
-- Optional (nil allowed)
local maybeString = Asserts.Optional(Asserts.String)

-- Default value when nil
local withDefault = Asserts.Default(Asserts.Integer, 0)

-- Union types (first match wins)
local stringOrNumber = Asserts.AnyOf(Asserts.String, Asserts.Number)

-- Intersection (all must pass)
local positiveFinite = Asserts.AllOf(Asserts.Positive, Asserts.Finite)

-- Exact value match
local validateVersion = Asserts.Equals(1)

-- Set membership
local validateRarity = Asserts.Set({"Common", "Rare", "Epic", "Legendary"})

-- String to number conversion
local parseInteger = Asserts.ToNumber(Asserts.Integer)
```

## Special Validators

```luau
-- DataStore-compatible types
Asserts.Storable(data) -- boolean | number | string | buffer | nested tables

-- Network-replicable types (includes Roblox types)
Asserts.Networkable(data) -- Storable + CFrame, Vector3, Instance, etc.

-- Table without metatable
Asserts.NoMetatable(t)
Asserts.AnyTable(t) -- Allows metatables
```

## Predicate Functions

For conditional logic without throwing:

```luau
if Asserts.IsFinite(x) then ... end
if Asserts.IsInteger(x) then ... end
if Asserts.IsASCII(s) then ... end
if Asserts.IsCFrameFinite(cf) then ... end
if Asserts.IsVector2Finite(v) then ... end
if Asserts.IsVector3Finite(v) then ... end
```

## Exported Types

```luau
Asserts.Map<K, V>            -- Type returned by Map validator
Asserts.MapCoerce<K, V, K2, V2> -- Type returned by MapCoerce validator
Asserts.Table<T>             -- Type returned by Table validator
Asserts.TableCoerce<T, T2>  -- Type returned by TableCoerce validator
Asserts.Storable             -- DataStore-compatible value type
Asserts.Networkable          -- Network-replicable value type
```

## Error Handling

Validators throw descriptive errors with key paths:

```luau
-- Error: "Integer $[2]" (second array element failed)
-- Error: "String $["name"]" (name field failed)
-- Error: "Range(1,100) $["config"]["port"]" (nested path)
```

Use `pcall` to catch validation errors:

```luau
local success, result = pcall(Asserts.Table({
    id = Asserts.UUID,
}), untrustedInput)

if not success then
    warn("Validation failed:", result)
end
```