It’s dangerous to conflate foo?.let { bar(it) } ?: baz() with if (foo != null) bar(foo) else baz(). Say you have a function: fun computeElements(): List<Int>? = emptyList() Consider this code: val maxElement = computeElements()?.let { it.max() } ?: return println(“Max element was $maxElement”) Compared to: val list: List<Int>? = computeElements() val maxElement = if … Read more
You can use isNullOrEmpty or its friend isNullOrBlank like so: if(!s.isNullOrEmpty()){ // s is not empty } Both isNullOrEmpty and isNullOrBlank are extension methods on CharSequence? thus you can use them safely with null. Alternatively turn null into false like so: if(s?.isNotEmpty() ?: false){ // s is not empty } you can also do the … Read more
You can also use the @Value annotation within the constructor: class Test( @Value(“\${my.value}”) private val myValue: Long ) { //… } This has the benefit that your variable is final and none-nullable. I also prefer constructor injection. It can make testing easier.
For some simple actions you can use the safe call operator, assuming the action also respects not operating on an empty list (to handle your case of both null and empty: myList?.forEach { …only iterates if not null and not empty } For other actions. you can write an extension function — two variations depending … Read more
You can use the elvis operator and evaluate another block of code with run { … }: data?.let { // execute this block if not null } ?: run { // execute this block if null } But this seems not to be quite as readable as a simple if–else statement. Also, you might find … Read more
A structural equality a == b is translated to a?.equals(b) ?: (b === null) Therefore when comparing to null, the structural equality a == null is translated to a referential equality a === null. According to the docs, there is no point in optimizing your code, so you can use a == null and a … Read more
This is unsafe nullable type (T?) conversion to a non-nullable type (T), !! will throw NullPointerException if the value is null. It is documented here along with Kotlin means of null-safety.