unwrapping the return Promise of then

[weironghuang31]

Hey there,

kovenant is a great library. I love to use it. However, there is a small feature I like I wish you can provide is "unwrap the return Promise of then"

For example, I have two methods

fun method1() : Promise<String, Exception>{}
fun method2() : Promise<String, Exception>{}

// current
val p: Promise<Promise<String, Exception>, Exception> = method1().then{ method2() }
// can it just be 
val p: Promise<String, Exception> = method1().then{ method2() }

Now, I added these extensions in my project to achieve it, but I don't know whether it is a good way to do it and it is a little unclear to use thenFlat instead of then.

infix fun <V, R> Promise<V, Exception>.thenFlat(bind: (V) -> Promise<R, Exception>): Promise<R, Exception> {
    val deferred = deferred<R, Exception>(context)
    success {
        try {
            bind(it).success(deferred::resolve).fail(deferred::reject)
        } catch (e: Exception) {
            deferred.reject(ApiError(e))
        }
    }.fail(deferred::reject)
    
    return deferred.promise
}

// so it can be
val p: Promise<String, Exception> = method1().thenFlat{ method2() }

[denisftw]

@wadehuang36 I'm not sure about the core package, but you can use bind from kovenant-functional. I wish the function was called flatMap instead of bind.