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 references are handled when both structures are circular at the same depth.

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

• Results are cached per object pair in a WeakMap. Objects must not be mutated after their first comparison.
• Map and Set comparisons are O(n²) in size.

Example (Comparing values)

import { Equal } from "effect"

// Primitives
console.log(Equal.equals(1, 1))         // true
console.log(Equal.equals(NaN, NaN))     // true
console.log(Equal.equals("a", "b"))     // false

// Objects and arrays
console.log(Equal.equals({ a: 1, b: 2 }, { a: 1, b: 2 })) // true
console.log(Equal.equals([1, [2, 3]], [1, [2, 3]]))         // true

// Dates
console.log(Equal.equals(new Date("2024-01-01"), new Date("2024-01-01"))) // true

// Maps (order-independent)
const m1 = new Map([["a", 1], ["b", 2]])
const m2 = new Map([["b", 2], ["a", 1]])
console.log(Equal.equals(m1, m2)) // true

// Curried form
const is5 = Equal.equals(5)
console.log(is5(5)) // true
console.log(is5(3)) // false