Скачать или смотреть Understanding ClosedRange and the Absence of in Operator in Kotlin: A Deep Dive

Discover why the `ClosedRange in ClosedRange` operation is not defined in Kotlin and learn how to create your own extension functions to solve this issue effectively.
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Understanding ClosedRange and the Absence of in Operator in Kotlin: A Deep Dive

When working with Kotlin on Android, you may have encountered an interesting problem regarding the ClosedRange operator. You might have noticed that using the expression a..b in x..y is invalid, while the expression (a..b).toRange() in (x..y).toRange() works perfectly. But why is there no operation like ClosedRange in ClosedRange? Let's explore this perplexing question and how to get around it.

The Problem Explained

To put it simply, ClosedRange and Range are two different concepts that belong to separate libraries. ClosedRange comes from Kotlin's standard library, while Range is part of the Android SDK. Here are a few important details that help clarify the situation:

Kotlin's ClosedRange: This can include negative sequences where the start value can be greater than the end value.

Android's Range: This is designed to disallow ranges that start with a higher number than they end with, making it impossible to have a negative range.

Because these two classes have different origins and purposes, attempts to use them interchangeably lead to the confusion we are addressing.

Why is There No in Operator for ClosedRange?

Possible Reasons

Several questions arise when faced with this limitation:

Is it an Oversight?: Given that ClosedRange and Range are maintained by different teams, it is not necessarily an oversight. The Kotlin development team may have left out this operator due to potential ambiguity regarding 'containment' of ranges.

Deliberate Decision: The definition of what constitutes a range in Kotlin may differ significantly from Android's definition, leading to different functionality. Kotlin's developers may have determined that the meaning of a ClosedRange containing another ClosedRange could be too complex or ambiguous.

Ambiguity of Negative Ranges: Since ClosedRange allows negative sequences, the concept of one ClosedRange being “in” another could lead to unclear results. Manipulating negative ranges would have different interpretations compared to positive ones.

Solutions: Custom Extension Functions

If you find yourself needing the functionality of ClosedRange in ClosedRange, you can create your own extension function. Here’s how you can approach it:

Create Your Own Containment Logic

You can customize the behavior based on your interpretation of how ranges should interact with each other. Here are a few examples of what your custom logic might look like:

[[See Video to Reveal this Text or Code Snippet]]

This keeps the standard containment logic intact. Alternatively, if you want to allow for empty ranges:

[[See Video to Reveal this Text or Code Snippet]]

A More Flexible Approach

For those who wish to accommodate both empty ranges and non-empty ranges, consider the following extension:

[[See Video to Reveal this Text or Code Snippet]]

This solution allows for more versatility in handling various scenarios regarding range containment.

Conclusion

In summary, the absence of a ClosedRange in ClosedRange operator in Kotlin stems from the differing philosophies behind ClosedRange and Range. Rather than being an oversight, it is likely a deliberate choice influenced by the two libraries’ differing requirements. However, with custom extension functions, you can implement the containment logic that best suits your application's needs on Android.

Now, you can leverage custom ranges confidently, knowing the background behind the design decisions in Kotlin!