Compiler error when comparing two arrays of structs in Swift

CompareTest.swift

//
//  CompareTest.swift
//
//  Created by Allen Ussher on 10/28/17.
//  Copyright © 2017 Ussher Press. All rights reserved.
//

import Foundation

struct StructWithValue {
    let value: Int
    
    init(value: Int) {
        self.value = value
    }
}

func ==(lhs: StructWithValue, rhs: StructWithValue) -> Bool {
    return lhs.value == rhs.value
}

struct StructWithArray {
    let array: [StructWithValue]

    init(array: [StructWithValue]) {
        self.array = array
    }
}

func ==(lhs: StructWithArray, rhs: StructWithArray) -> Bool {
    // Compiler error here: Binary operator '==' cannot be applied to two '[StructWithValue]' operands
    return lhs.array == rhs.array
}

FixedVersion.swift

// Well, it works if you make the structs Equatable. Silly me.

import Foundation

struct StructWithValue: Equatable {
    let value: Int
    
    init(value: Int) {
        self.value = value
    }

    static func ==(lhs: StructWithValue, rhs: StructWithValue) -> Bool {
        return lhs.value == rhs.value
    }
}

struct StructWithArray: Equatable {
    let array: [StructWithValue]

    init(array: [StructWithValue]) {
        self.array = array
    }

    static func ==(lhs: StructWithArray, rhs: StructWithArray) -> Bool {
        // Compiler error here: Binary operator '==' cannot be applied to two '[StructWithValue]' operands
        return lhs.array == rhs.array
    }
}

The compiler error on line 32 of CompareTest.swift makes me sad. :(

But if you make them Equatable, it works fine. :)