<T>(): Transformation<Option.Option<T>, T | null>Decodes T | null into Option<T> and encodes Option<T> back to
T | null.
When to use
Use when you need a schema transformation to convert nullable API fields to
Option.
Details
Decoding maps null to Option.none() and non-null values to
Option.some(value). Encoding maps Option.none() to null and
Option.some(value) to value. The transformation is pure and synchronous.
Example (Converting nullable values to an Option)
import { Schema, SchemaTransformation } from "effect"
const schema = Schema.NullOr(Schema.String).pipe(
Schema.decodeTo(
Schema.Option(Schema.String),
SchemaTransformation.optionFromNullOr()
)
)export function function optionFromNullOr<
T
>(): Transformation<Option.Option<T>, T | null>
Decodes T | null into Option<T> and encodes Option<T> back to
T | null.
When to use
Use when you need a schema transformation to convert nullable API fields to
Option.
Details
Decoding maps null to Option.none() and non-null values to
Option.some(value). Encoding maps Option.none() to null and
Option.some(value) to value. The transformation is pure and synchronous.
Example (Converting nullable values to an Option)
import { Schema, SchemaTransformation } from "effect"
const schema = Schema.NullOr(Schema.String).pipe(
Schema.decodeTo(
Schema.Option(Schema.String),
SchemaTransformation.optionFromNullOr()
)
)
optionFromNullOr<function (type parameter) T in optionFromNullOr<T>(): Transformation<Option.Option<T>, T | null>T>(): class Transformation<in out T, in out E, RD = never, RE = never>class Transformation {
_tag: 'Transformation';
decode: SchemaGetter.Getter<T, E, RD>;
encode: SchemaGetter.Getter<E, T, RE>;
flip: () => Transformation<E, T, RE, RD>;
compose: <T2, RD2, RE2>(other: Transformation<T2, T, RD2, RE2>) => Transformation<T2, E, RD | RD2, RE | RE2>;
}
Represents a bidirectional transformation between a decoded type T and an encoded
type E, built from a pair of Getters.
When to use
Use when you need a schema transformation that defines how a schema converts
between two representations.
- You want to compose multiple transformations into a pipeline.
- You want to flip a transformation to swap decode/encode.
Details
This is the primary building block for Schema.decodeTo, Schema.encodeTo,
Schema.decode, Schema.encode, and Schema.link. Each direction is a
SchemaGetter.Getter that handles optionality, failure, and Effect services.
- Immutable —
flip() and compose() return new instances.
flip() swaps the decode and encode getters.compose(other) chains: this.decode then other.decode for decoding,
other.encode then this.encode for encoding.
Example (Composing two transformations)
import { SchemaTransformation } from "effect"
const trimAndLower = SchemaTransformation.trim().compose(
SchemaTransformation.toLowerCase()
)
// decode: trim then lowercase
// encode: passthrough (both directions)
Transformation<import OptionOption.type Option<A> = Option.None<A> | Option.Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) T in optionFromNullOr<T>(): Transformation<Option.Option<T>, T | null>T>, function (type parameter) T in optionFromNullOr<T>(): Transformation<Option.Option<T>, T | null>T | null> {
return function transform<T, E>(options: {
readonly decode: (input: E) => T
readonly encode: (input: T) => E
}): Transformation<T, E>
Creates a Transformation from pure (sync, infallible) decode and encode
functions.
When to use
Use when you need an infallible schema transformation that does not require
Effect services.
Details
- Each function receives the input and returns the output directly.
- Skips
None inputs (missing keys) — functions are only called on present values.
- Does not allocate Effects internally; uses optimized sync path.
Example (Converting between cents and dollars)
import { Schema, SchemaTransformation } from "effect"
const CentsFromDollars = Schema.Number.pipe(
Schema.decodeTo(
Schema.Number,
SchemaTransformation.transform({
decode: (dollars) => dollars * 100,
encode: (cents) => cents / 100
})
)
)
transform({
decode: <A>(a: A) => Option<Exclude<A, null>>decode: import OptionOption.const fromNullOr: <A>(
a: A
) => Option<Exclude<A, null>>
Converts a possibly null value into an Option, leaving undefined
as a valid Some.
When to use
Use when you want to treat only null as absent while preserving
undefined as a meaningful value.
Details
null → None- Any other value (including
undefined) → Some
Example (Converting possibly null values to an Option)
import { Option } from "effect"
console.log(Option.fromNullOr(null))
// Output: { _id: 'Option', _tag: 'None' }
console.log(Option.fromNullOr(undefined))
// Output: { _id: 'Option', _tag: 'Some', value: undefined }
console.log(Option.fromNullOr(42))
// Output: { _id: 'Option', _tag: 'Some', value: 42 }
fromNullOr,
encode: <A>(self: Option<A>) => A | nullencode: import OptionOption.const getOrNull: <A>(
self: Option<A>
) => A | null
Extracts the value from a Some, or returns null for None.
When to use
Use when you need to pass absent Option values to APIs that expect null.
Details
Some → the inner valueNone → null
Example (Unwrapping to null)
import { Option } from "effect"
console.log(Option.getOrNull(Option.some(1)))
// Output: 1
console.log(Option.getOrNull(Option.none()))
// Output: null
getOrNull
})
}