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android-studiokotlinintellij-ideaelvis-operator

If check with nullable boolean and elvis operator fails inspection check, why?

in Android Studio I wrote the following in a function:

if (startTimes.value?.containsKey(name)?:false) {
    return startTimes?.value?.get(name)
}

Android Studio highlights the contents of the if with a warning with the message Equality check should be used instead of elvis for nullable boolean check and suggests I replace it with:

if (startTimes.value?.containsKey(name) == true) {
    return startTimes?.value?.get(name)
}

Why is the second preferred by the IDE? As far as I can tell they're logically the same.

Solution

  • Checking nullable boolean against true or false is an "official" Kotlin idiom:

    Nullable Boolean

    val b: Boolean? = ... 
if (b == true) {
    ... 
} else {
    // `b` is false or null 
}

    Here is the relevant discussion regarding the idiom, including opinions for and against it.