API / Core / Null

Null

t

RESCRIPT
type t<'a> = Js.Null.t<'a>

A type representing a value that can be either 'a or null.

asNullable

RESCRIPT
let asNullable: t<'a> => Core__Nullable.t<'a>

Converts a Null.t into a Nullable.t.

Examples

RESCRIPT
let nullValue = Null.make("Hello") let asNullable = nullValue->Null.asNullable // Nullable.t<string>

null

RESCRIPT
let null: t<'a>

The value null.

See null on MDN.

Examples

RESCRIPT
Console.log(null) // Logs `null` to the console.

make

RESCRIPT
let make: 'a => t<'a>

Creates a new Null.t from the provided value. This means the compiler will enforce null checks for the new value.

Examples

RESCRIPT
let myStr = "Hello" let asNullValue = myStr->Null.make // The compiler now thinks this can be `string` or `null`.

equal

RESCRIPT
let equal: (t<'a>, t<'b>, ('a, 'b) => bool) => bool

compare

RESCRIPT
let compare: ( t<'a>, t<'b>, ('a, 'b) => Core__Ordering.t, ) => Core__Ordering.t

toOption

RESCRIPT
let toOption: t<'a> => option<'a>

Converts a nullable value into an option, so it can be pattern matched on. Will convert null to None, and a present value to Some(value).

Examples

RESCRIPT
let nullStr = Null.make("Hello") switch nullStr->Null.toOption { | Some(str) => Console.log2("Got string:", str) | None => Console.log("Didn't have a value.") }

fromOption

RESCRIPT
let fromOption: option<'a> => t<'a>

Turns an option into a Null.t. None will be converted to null.

Examples

RESCRIPT
let optString: option<string> = None let asNull = optString->Null.fromOption // Null.t<string> Console.log(asNull == null) // Logs `true` to the console.

getOr

RESCRIPT
let getOr: (t<'a>, 'a) => 'a

getOr(value, default) returns value if not null, otherwise return default.

Examples

RESCRIPT
Null.getOr(null, "Banana") // Banana Null.getOr(Nulalble.make("Apple"), "Banana") // Apple let greet = (firstName: option<string>) => "Greetings " ++ firstName->Null.getOr("Anonymous") Null.make("Jane")->greet // "Greetings Jane" null->greet // "Greetings Anonymous"

getWithDefault

Deprecated

Use getOr instead

RESCRIPT
let getWithDefault: (t<'a>, 'a) => 'a

getExn

RESCRIPT
let getExn: t<'a> => 'a

getExn(value) raises an exception if null, otherwise returns the value.

RESCRIPT
Null.getExn(Null.make(3)) // 3 Null.getExn(null) /* Raises an Error */

Exceptions

  • Raises Invalid_argument if value is null,

getUnsafe

RESCRIPT
let getUnsafe: t<'a> => 'a

getUnsafe(value) returns value.

Examples

RESCRIPT
Null.getUnsafe(Null.make(3)) == 3 Null.getUnsafe(null) // Raises an error

Important

  • This is an unsafe operation, it assumes value is not null.

forEach

RESCRIPT
let forEach: (t<'a>, 'a => unit) => unit

forEach(value, f) call f on value. if value is not null, then if calls f, otherwise returns unit.

Examples

RESCRIPT
Null.forEach(Null.make("thing"), x => Console.log(x)) // logs "thing" Null.forEach(null, x => Console.log(x)) // returns ()

map

RESCRIPT
let map: (t<'a>, 'a => 'b) => t<'b>

map(value, f) returns f(value) if value is not null, otherwise returns value unchanged.

Examples

RESCRIPT
Null.map(Null.make(3), x => x * x) // Null.make(9) Null.map(null, x => x * x) // null

mapOr

RESCRIPT
let mapOr: (t<'a>, 'b, 'a => 'b) => 'b

mapOr(value, default, f) returns f(value) if value is not null, otherwise returns default.

Examples

RESCRIPT
let someValue = Null.make(3) someValue->Null.mapOr(0, x => x + 5) // 8 let noneValue = null noneValue->Null.mapOr(0, x => x + 5) // 0

mapWithDefault

Deprecated

Use mapOr instead

RESCRIPT
let mapWithDefault: (t<'a>, 'b, 'a => 'b) => 'b

flatMap

RESCRIPT
let flatMap: (t<'a>, 'a => t<'b>) => t<'b>

flatMap(value, f) returns f(value) if value is not null, otherwise returns value unchanged.

Examples

RESCRIPT
let addIfAboveOne = value => if (value > 1) { Null.make(value + 1) } else { null } Null.flatMap(Null.make(2), addIfAboveOne) // Null.make(3) Null.flatMap(Null.make(-4), addIfAboveOne) // null Null.flatMap(null, addIfAboveOne) // null