LazyCached

Simple library, that adds possibility of caching to Kotlin's lazy.

Check examples

Gradle

Maven

Example

For example, imagine we have some resource-intensive operation:

import lazyCached

/**
 * Represents some operation, that requires a lot of time to execute with caching and lazy invocation.
 * On calling [result] it just forces thread to sleep for [sleepTime] milliseconds.
 * On changing [sleepTime] next [result] call should recalculate again.
 * @param startingSleepTime time in milliseconds for thread sleep.
 */
class SimpleCachedResourceIntensiveOperation(startingSleepTime: Long) {

    /**
     * Flag for caching
     */
    private var cached = false
    
    /**
     * Time in milliseconds for thread to sleep
     * Not final!
     */
    public var sleepTime = startingSleepTime
        set(value) {
            field = value
            cached = false
        }

    /**
     * Forces thread to sleep if [cached] is False.
     * Then sets [cached] flag to true and returns [sleepTime].
     * Else, just returns cached [sleepTime].
     */
    public val result: Number by lazyCached(
            {
                Thread.sleep(sleepTime)
                cached = true
                sleepTime
            },
            { !cached }
    )

}

In this case, on changing sleepTime it is required to recalculate result, but it is better to do it in a lazy way.

This problem is solved with lazyCached.

First argument of lazyCached delegate is same as for lazy.
Second argument is some condition, that returns True or False, where True forces first argument to be revoked again.
Third argument is same lock as for lazy.

More examples
Tests

Imports

Get into Gradle

Add it in your root build.gradle at the end of repositories:

allprojects {
    repositories {
        ...
        maven { url 'https://jitpack.io' }
    }
}

Add the dependency

dependencies {
    implementation 'com.github.sikrinick:lazy-cached:v1.0.0'
}

Get into Maven

<repositories>
    <repository>
        <id>jitpack.io</id>
        <url>https://jitpack.io</url>
    </repository>
</repositories>