Lambda's are ignored until "run" is added

Question

I have an rx chain that calls an API through Retrofit. I subscribe to my API service, with standard rx subscribe({...}) method and pass a lambda to it. Unfortunately when my call is finally completed, all the code I have added to be executed inside lambda is totally ignored. AndroidStudio suggested a fix which basically adds an inline function run to my lamda and... it magically works. I have no idea what's happening. Why does it not work without run? What does run do?

The code follows:

valuesServiceApi.getValues()
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe({ data ->
                run { //<- What's this?
                    val cs = data.creditReportInfo.score
                    view.setCreditScore(cs)
                    Logger.getLogger("success:").info("credit score $cs")
                }

            })

Answer 1

{ expressions } is a short form of { -> expressions }, which is a function literal with zero parameters.

Therefore,

{ data ->
    {
        val cs = data.creditReportInfo.score
        view.setCreditScore(cs)
        Logger.getLogger("success:").info("credit score $cs")
     }
}

is the same as

{ data ->
    { ->
        val cs = data.creditReportInfo.score
        view.setCreditScore(cs)
        Logger.getLogger("success:").info("credit score $cs")
    }
}

which creates a lambda expression, and do nothing with it.

What you want to do is

{ data ->
    { ->
        val cs = data.creditReportInfo.score
        view.setCreditScore(cs)
        Logger.getLogger("success:").info("credit score $cs")
    }()
}

but this does the same as

{ data ->
    val cs = data.creditReportInfo.score
    view.setCreditScore(cs)
    Logger.getLogger("success:").info("credit score $cs")
}

plus additional function creation overhead.

run { ... } is the same as { ... }() minus additional temporary function creation overhead. So the above is the same as

{ data ->
    run { ->
        val cs = data.creditReportInfo.score
        view.setCreditScore(cs)
        Logger.getLogger("success:").info("credit score $cs")
    }
}