Hi, is there a way to pass @launch to another function? I have this piece ```viewModelScope.launch {...

# coroutines

[Lena Stepanova]

Hi, is there a way to pass @launch to another function? I have this piece

viewModelScope.launch { 
    validateEmail(user)?.let {
        _errorLiveData.postValue(it)
        stopLoading()
        return@launch
    }
}

And I want it to look something like

evaluate(validateEmail(user), launch)

with

fun evaluate(result: String?, job: (
    context: CoroutineContext,
    start: CoroutineStart,
    block: suspend CoroutineScope.() -> Unit
) -> Job){
    result?.let {
        _errorLiveData.postValue(it)
        stopLoading()
        return@job
    }
}

I get job is unresolved, so what am I doing wrong and how to make it right?

[wasyl]

Can you clarify what you want to achieve? I don’t quite understand from the snippets you pasted

[Lena Stepanova]

I have a number of blocks like

validateIpData(it)?.let {
    _errorLiveData.postValue(it)
    return@launch
}

Inside viewmodelScope.launch:

viewModelScope.launch {
    // if cloud login, validate username as email
    validateEmail(user)?.let {
        _errorLiveData.postValue(it)
        stopLoading()
        return@launch
    }
    
    loginModel.login(user)?.let { it ->
        _errorLiveData.postValue(it)
        return@launch
    }
    // if success, move to device list view
    _navigateToDeviceList.postValue(username.value)
}

And I want to make it more readable

[wasyl]

I don’t have any idea right now 😕 But I’d suggest avoiding multiple returns and non-local returns and either returning Boolean from your validation functions or e.g. throwing an exception if validation fails. Keeping it simple would probably help readability more than a fancy evaluate function which takes a while to understand in couple of months 🙂

[myanmarking]

i dont quite get it. Why would you want to return the launch block? I dont think that is what you want

[myanmarking]

basically from what i understand, if validateEmail is not null, and login is not null, you want to display an error. I think that design could be improved a bit 😛 Generally, it’s the other way around

[myanmarking]

personnally, for you usecase, i find plain old java more readable:

[myanmarking]

viewModelScope.launch {
val emailError = validateEmail(user)
if(emailError != null){
_errorLiveData.postValue(it)
stopLoading()
return@launch
}
val loginError = loginModel.login(user)
if(loginError != null){
_errorLiveData.postValue(it)
return@launch
}
_navigateToDeviceList.postValue(username.value)
}

[myanmarking]

because the original code is a bit confusing to read. Yes, it is less code, but less readable as well

[myanmarking]

if you cannot change the design, just extract the code inside launch to a suspending function, and there you can just return

[myanmarking]

viewModelScope.launch {
if(login()){
_navigateToDeviceList.postValue(username.value)
}
}
suspend fun login(): Boolean
validateEmail(user)?.let {
_errorLiveData.postValue(it)
stopLoading()
return false
}
loginModel.login(user)?.let { it ->
_errorLiveData.postValue(it)
return false
}
}

[myanmarking]

something like this!

[Lena Stepanova]

There is still a number of blocks

{
        _errorLiveData.postValue(it)
        stopLoading()
        return@launch
    }

And there are actually more validations, which I wanted to make less pronounced, so that it basically reads like {
validateEmail()
validateUsername()
validateIp()
...
}

[Lena Stepanova]

Using suspend function looks like a good idea, I'll try it out, thanks!

[myanmarking]

how about this

[myanmarking]

viewModelScope.launch {
val loginError = login()
if(loginError == null){
_navigateToDeviceList.postValue(username.value)
} else{
_errorLiveData.postValue(loginError)
stopLoading()
}
}

suspend fun login(): Error?
return validateEmail(user)
?: loginModel.login(user)
?: null
}

[myanmarking]

or this

[myanmarking]

viewModelScope.launch {
login()?.let{
_errorLiveData.postValue(loginError)
stopLoading()
} ?: _navigateToDeviceList.postValue(username.value)
}

suspend fun login(): Error
return validateEmail(user)
?: loginModel.login(user)
?: null
}

[myanmarking]

but less readable imo. It’s a matter of preference