effect-io-ai

Package: effect
Module: Fiber

Fiber.Fiber.Variance

Variance encoding for the Fiber type, specifying covariance in both the success type A and the error type E.

When to use

Use to carry the success and error type parameters for Fiber in Effect’s type machinery.

Example (Upcasting fibers safely)

import type { Fiber } from "effect"

// Variance allows safe subtyping
declare const fiber: Fiber.Fiber<number, Error>
const upcast: Fiber.Fiber<unknown, unknown> = fiber

Signature

export interface Variance<out A, out E = never> {
    readonly _A: Covariant<A>
    readonly _E: Covariant<E>
  }

Source

Since v2.0.0