Hi everyone :wave: I recently open-sourced a Kotl...

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[Abraham Golor]

Hi everyone 👋

I recently open-sourced a Kotlin Multiplatform library called phonenumber for phone number validation and formatting across Android and iOS.

Why I built it:
While working on a KMP app, I found myself duplicating phone number validation logic across Android and iOS. Android had libphonenumber, iOS had PhoneNumberKit, and keeping behavior consistent between both platforms became messy.
So I built a shared KMP wrapper that exposes a single API while delegating to each platform’s native implementation.

Features:

- Global phone number validation
- Validation by country ISO code
- Validation by country calling code
- Format to E.164
- Format to international format
- Extract region code
- Extract country calling code
- Shared API for Android & iOS
- Native performance (libphonenumber on Android, PhoneNumberKit on iOS)

GitHub: https://github.com/ajayinnovations/phonenumber

Would love feedback on the API design, naming, and any edge cases I might have missed 🙏

[CLOVIS]

Feedback: you marked PhoneNumberInfo as a data class but it's likely that you will add new fields in the future. This is not recommended, see why → https://jakewharton.com/public-api-challenges-in-kotlin/

[CLOVIS]

Additionally, this allows users to write:

val info = PhoneNumberValidator.parse("[phone]")
    .copy(international = "whatever ahah")

which makes no sense.

[CLOVIS]

If two phone numbers are the same but formatted differently, it probably makes more sense that == reports them identical, but your existing implementation would report that they are different, so a Set<PhoneNumberInfo> would not work if the input format is different.

To solve all of these problems, you can structure it as:

public class PhoneNumberInfo internal constructor(
    val international: String?,
) {
    val e164 = PhoneNumberValidator.format(international, PhoneNumberFormat.E164)

    val regionCode = PhoneNumberValidator.regionCode(international)
    
    val countryCode = PhoneNumberValidator.countryCode(international)

    override fun toString() = "PhoneNumberInfo($international)"

    override fun equals(other: Any?): Boolean {
        return other is PhoneNumberInfo && international == other.international
    }

    override fun hashCode(): Int = international.hashCode()
}

// Fake constructor for convenience
fun PhoneNumberInfo(
    input: String,
) : PhoneNumberInfo(PhoneNumberValidator.format(input, PhoneNumberFormat.INTERNATIONAL))

You may add by lazy on some fields if they are expensive to compute.

At this point, you may call this type PhoneNumber instead of PhoneNumberInfo , since it contains all info for a phone number.

[CLOVIS]

And then if you want to push it further, all methods of PhoneNumberValidator could be moved into PhoneNumber 's companion object , but it objectively doesn't change much, it's a matter of taste and your preference. The upside is that the entire library can fit in one less public type.

[Abraham Golor]

Hello,
I really appreciate your feedback and I will implement it in the upcoming version coming out in a few days 🙏

[CLOVIS]

If you want, you can send me the PR in DM and I'll review it