Throwable is not comparable :/

[Arnaud Giuliani]

Hello,

the fact that Throwable is not comparable as is in Kotlin is a big problem. It forces us to make some workaround to make it "comparable".

If we check what is a comparable:

/**
 * The base class for all errors and exceptions. Only instances of this class can be thrown or caught.
 *
 * @param message the detail message string.
 * @param cause the cause of this throwable.
 */
public open class Throwable(open val message: String?, open val cause: Throwable?) {
    constructor(message: String?) : this(message, null)

    constructor(cause: Throwable?) : this(cause?.toString(), cause)

    constructor() : this(null, null)
}

I would propose then a data class type to encapsulate Throwable:

open class ThrowableKt(val message: String? = null, val cause: ThrowableKt? = null) {

    constructor(message: String? = null) : this(message, null as? ThrowableKt)
    constructor(message: String? = null, cause: Throwable? = null) : this(message, cause?.toThrowableKt())
    constructor(message: String? = null, cause: Exception? = null) : this(message, cause?.toThrowableKt())

    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (javaClass != other?.javaClass) return false

        other as ThrowableKt

        if (message != other.message) return false
        if (cause != other.cause) return false

        return true
    }

    override fun hashCode(): Int {
        var result = message?.hashCode() ?: 0
        result = 42 * result + (cause?.hashCode() ?: 0)
        return result
    }

    override fun toString(): String = "ThrowableKt(message='$message',cause=$cause)"
}

fun Throwable.toThrowableKt(): ThrowableKt {
    return ThrowableKt(message, cause?.toThrowableKt())
}

fun throwableKt(t: Throwable) = t.toThrowableKt()

What do you think?

[Arnaud Giuliani]

it would make all state comparison more easy, and also less painful for users to implement their own state failure as they don't need to override Equals to compare Exception/Throwable

[Arnaud Giuliani]

state and event can be written like that:

data class Failed(val message: String? = null, val error: ThrowableKt? = null, val state: UIState? = null) : UIState() {
        constructor(message: String? = null) : this(message, null as ThrowableKt)
        constructor(message: String? = null, state: UIState? = null) : this(message, null as ThrowableKt, state)
        constructor(message: String? = null, error: Throwable? = null, state: UIState? = null) : this(message, error?.toThrowableKt(), state)
        constructor(message: String? = null, error: Exception? = null, state: UIState? = null) : this(message, error?.toThrowableKt(), state)
    }

[Arnaud Giuliani]

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