/**
 * Compares values with Effect's structural equality rules.
 *
 * `equals` compares primitives, arrays, plain objects, maps, sets, dates,
 * regular expressions, and values that implement the `Equal` interface. This
 * module also defines the equality symbol, guards, adapters, map and set
 * comparison builders, and helpers for marking objects that should compare only
 * by reference.
 *
 * @stability stable
 * @since 2.0.0
 */
import type { Equivalence } from "./Equivalence.ts";
import * as Hash from "./Hash.ts";
/**
 * Defines the unique string identifier for the `Equal` interface.
 *
 * **When to use**
 *
 * Use when you implement custom equality and need the computed property key for
 * the equality method.
 *
 * **Details**
 *
 * This is a pure constant with no allocation or side effects.
 *
 * **Example** (Implementing Equal on a class)
 *
 * ```ts import.meta.vitest
 * import { Equal, Hash } from "effect"
 *
 * class UserId implements Equal.Equal {
 *   constructor(readonly id: string) {}
 *
 *   [Equal.symbol](that: Equal.Equal): boolean {
 *     return that instanceof UserId && this.id === that.id
 *   }
 *
 *   [Hash.symbol](): number {
 *     return Hash.string(this.id)
 *   }
 * }
 *
 * Equal.equals(new UserId("1"), new UserId("1")) // => true
 * Equal.equals(new UserId("1"), new UserId("2")) // => false
 * ```
 *
 * @see {@link Equal} — the interface that uses this symbol
 * @see {@link isEqual} — type guard for `Equal` implementors
 * @stability stable
 * @category symbols
 * @since 2.0.0
 */
export declare const symbol = "~effect/Equal";
/**
 * The interface for types that define their own equality logic.
 *
 * **When to use**
 *
 * Use when you need value-based equality for a class (e.g. domain IDs,
 *   coordinates, money values).
 * - When your type will be stored in `HashMap` or `HashSet`.
 * - When the default structural comparison is too broad or too narrow for
 *   your type.
 *
 * **Details**
 *
 * Any object that implements both `[Equal.symbol]` (equality) and
 * `[Hash.symbol]` (hashing) is recognized by {@link equals} and by hash-based
 * collections such as `HashMap` and `HashSet`.
 *
 * - Extends `Hash.Hash`, so implementors **must** also provide `[Hash.symbol]`.
 * - The hash contract: if `a[Equal.symbol](b)` returns `true`, then
 *   `Hash.hash(a)` must equal `Hash.hash(b)`.
 * - {@link equals} delegates to this method when both operands implement it.
 *   If only one operand implements `Equal`, they are considered unequal.
 *
 * **Example** (Comparing coordinates by value)
 *
 * ```ts import.meta.vitest
 * import { Equal, Hash } from "effect"
 *
 * class Coordinate implements Equal.Equal {
 *   constructor(readonly x: number, readonly y: number) {}
 *
 *   [Equal.symbol](that: Equal.Equal): boolean {
 *     return that instanceof Coordinate &&
 *       this.x === that.x &&
 *       this.y === that.y
 *   }
 *
 *   [Hash.symbol](): number {
 *     return Hash.string(`${this.x},${this.y}`)
 *   }
 * }
 *
 * Equal.equals(new Coordinate(1, 2), new Coordinate(1, 2)) // => true
 * Equal.equals(new Coordinate(1, 2), new Coordinate(3, 4)) // => false
 * ```
 *
 * @see {@link symbol} — the property key used by the equality method
 * @see {@link equals} — the main comparison function
 * @see {@link isEqual} — type guard for `Equal` implementors
 * @stability stable
 * @category models
 * @since 2.0.0
 */
export interface Equal extends Hash.Hash {
    [symbol](that: Equal): boolean;
}
/**
 * Checks whether two values are deeply structurally equal.
 *
 * **When to use**
 *
 * Use when you need Effect's default structural equality check.
 *
 * **Details**
 *
 * Returns a `boolean` and never throws. Primitives are compared by value, and
 * `NaN` equals `NaN`. Objects implementing `Equal` delegate to their
 * `[Equal.symbol]` method; if only one operand implements `Equal`, the result
 * is `false`.
 *
 * Dates compare by ISO string, RegExps compare by string representation,
 * arrays compare element-by-element, Maps and Sets compare entries
 * order-independently, and plain objects compare enumerable keys recursively.
 * Functions without an `Equal` implementation compare by reference. Circular
 * structures use coinductive equality.
 *
 * Hash values are checked first as a fast-path rejection. The function also
 * supports dual data-last usage: call it with one argument to get a curried
 * predicate.
 *
 * **Gotchas**
 *
 * - Object-pair results are cached in a WeakMap. **Objects must not be
 *   be mutated after their first comparison.**
 * - Map and Set entries are matched within groups of equal hashes, so they
 *   are O(n) for well-distributed hashes and O(n²) when every hash collides.
 *
 * **Example** (Comparing values)
 *
 * ```ts import.meta.vitest
 * import { Equal } from "effect"
 *
 * Equal.equals(1, 1) // => true
 * Equal.equals(NaN, NaN) // => true
 * Equal.equals("a", "b") // => false
 *
 * Equal.equals({ a: 1, b: 2 }, { a: 1, b: 2 }) // => true
 * Equal.equals([1, [2, 3]], [1, [2, 3]]) // => true
 *
 * Equal.equals(new Date("2024-01-01"), new Date("2024-01-01")) // => true
 *
 * const m1 = new Map([["a", 1], ["b", 2]])
 * const m2 = new Map([["b", 2], ["a", 1]])
 * Equal.equals(m1, m2) // => true
 *
 * const is5 = Equal.equals(5)
 * is5(5) // => true
 * is5(3) // => false
 * ```
 *
 * @see {@link Equal} — the interface for custom equality
 * @see {@link isEqual} — check whether a value implements `Equal`
 * @see {@link asEquivalence} — wrap `equals` as an `Equivalence`
 * @stability stable
 * @category equality
 * @since 2.0.0
 */
export declare function equals<B>(that: B): <A>(self: A) => boolean;
export declare function equals<A, B>(self: A, that: B): boolean;
/**
 * Checks whether a value implements the {@link Equal} interface.
 *
 * **When to use**
 *
 * Use when you need generic utility code to distinguish `Equal` implementors
 * from plain values before calling `[Equal.symbol]` directly.
 *
 * **Details**
 *
 * - Pure function, no side effects.
 * - Returns `true` if and only if `u` has a property keyed by
 *   {@link symbol}.
 * - Acts as a TypeScript type guard, narrowing the input to {@link Equal}.
 *
 * **Example** (Checking Equal values)
 *
 * ```ts import.meta.vitest
 * import { Equal, Hash } from "effect"
 *
 * class Token implements Equal.Equal {
 *   constructor(readonly value: string) {}
 *   [Equal.symbol](that: Equal.Equal): boolean {
 *     return that instanceof Token && this.value === that.value
 *   }
 *   [Hash.symbol](): number {
 *     return Hash.string(this.value)
 *   }
 * }
 *
 * Equal.isEqual(new Token("abc")) // => true
 * Equal.isEqual({ x: 1 }) // => false
 * Equal.isEqual(42) // => false
 * ```
 *
 * @see {@link Equal} — the interface being checked
 * @see {@link symbol} — the property key that signals `Equal` support
 * @stability stable
 * @category guards
 * @since 2.0.0
 */
export declare const isEqual: (u: unknown) => u is Equal;
/**
 * Wraps {@link equals} as an `Equivalence<A>`.
 *
 * **When to use**
 *
 * Use when you want to pass `Equal.equals` to APIs that require an
 * `Equivalence`.
 *
 * **Details**
 *
 * - Returns a function `(a: A, b: A) => boolean` that delegates to
 *   {@link equals}.
 * - Pure; allocates a thin wrapper on each call.
 *
 * **Example** (Deduplicating with Equal semantics)
 *
 * ```ts import.meta.vitest
 * import { Array, Equal } from "effect"
 *
 * Array.dedupeWith([1, 2, 2, 3, 1], Equal.asEquivalence<number>()) // => [1, 2, 3]
 * ```
 *
 * @see {@link equals} — the underlying comparison function
 * @stability stable
 * @category instances
 * @since 4.0.0
 */
export declare const asEquivalence: <A>() => Equivalence<A>;
/**
 * Creates a proxy that uses reference equality instead of structural equality.
 *
 * **When to use**
 *
 * Use when you need to compare a plain object or array by identity without
 * mutating the original value.
 *
 * **Details**
 *
 * - Returns a `Proxy` wrapping `obj`. The proxy reads through to the
 *   original, so property access is unchanged.
 * - The proxy is registered in an internal WeakSet; {@link equals} returns
 *   `false` for any pair where at least one operand is in that set (unless
 *   they are the same reference).
 * - Each call creates a **new** proxy, so `byReference(x) !== byReference(x)`.
 * - Does **not** mutate the original object (unlike {@link byReferenceUnsafe}).
 *
 * **Example** (Opting out of structural equality)
 *
 * ```ts import.meta.vitest
 * import { Equal } from "effect"
 *
 * const a = { x: 1 }
 * const b = { x: 1 }
 *
 * Equal.equals(a, b) // => true
 *
 * const aRef = Equal.byReference(a)
 * Equal.equals(aRef, b) // => false
 * Equal.equals(aRef, aRef) // => true
 * aRef.x // => 1
 * ```
 *
 * @see {@link byReferenceUnsafe} — same effect without a proxy (mutates the
 *   original)
 * @see {@link equals} — the comparison function affected by this opt-out
 * @stability stable
 * @category equality
 * @since 4.0.0
 */
export declare const byReference: <T extends object>(obj: T) => T;
/**
 * Marks an object permanently to use reference equality, without creating a proxy.
 *
 * **When to use**
 *
 * Use when you need reference equality without proxy allocation and accept
 * permanently marking the original object for reference-only equality.
 *
 * **Details**
 *
 * - Adds `obj` to an internal WeakSet. From that point on, {@link equals}
 *   treats it as reference-only.
 * - Returns the **same** object (not a copy or proxy), so
 *   `byReferenceUnsafe(x) === x`.
 * - Does **not** affect the object's prototype, properties, or behavior
 *   beyond equality checks.
 *
 * **Gotchas**
 *
 * The marking is irreversible for the lifetime of the object.
 *
 * **Example** (Marking an object for reference equality)
 *
 * ```ts import.meta.vitest
 * import { Equal } from "effect"
 *
 * const obj1 = { a: 1, b: 2 }
 * const obj2 = { a: 1, b: 2 }
 *
 * const marked = Equal.byReferenceUnsafe(obj1)
 *
 * Equal.equals(obj1, obj2) // => false
 * Equal.equals(obj1, obj1) // => true
 * marked === obj1 // => true
 * ```
 *
 * @see {@link byReference} — safer alternative that creates a proxy
 * @see {@link equals} — the comparison function affected by this opt-out
 * @stability stable
 * @category unsafe
 * @since 4.0.0
 */
export declare const byReferenceUnsafe: <T extends object>(obj: T) => T;
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