Quick Disclaimer & Guide

To add KTee in your project implement the two artifacts as follows.

repositories {		
    maven { url "https://jitpack.io" }
}

dependencies {
    debugImplementation 'com.github.rtsketo.ktee:yetee:1.0.2'
    releaseImplementation 'com.github.rtsketo.ktee:notee:1.0.2'
}

This repo is a modified version of Medly's Ktee which adds a noop implementation, the notee artifact.

KTee

KTee is Tee for Kotlin code pipelines. If you love the unix command line tee, you know what we mean.

Why?

Often times we need to break a perfect computation pipeline just to be able to log the intermediate values. For example, lets take a look at this code:

(1..10)
    .filter { it % 2 == 0 }
    .map { it * 2 }
    .reduce(Int::plus)

If we want to print the result of filter or map we need to either capture the result into an intermediate val or add a .let { } with logging statements.

KTee simplifies printing intermediate values dramatically.

How?

Just .tee() it. Seriously! Try this:

(1..10)
    .filter { it % 2 == 0 }.tee()
    .map { it * 2 }.tee()
    .reduce(Int::plus).tee()

Which produces following output on the console:

[2, 4, 6, 8, 10]
[4, 8, 12, 16, 20]
60

Can I Customize the output?

We can customize the way tee prints using markers and lambda blocks to return custom log messages.

(1..10)
    .filter { it % 2 == 0 }.tee("even numbers: ")
    .map { it * 2 }.tee("doubles >>>>> ")
    .reduce(Int::plus).tee {"the result is $it"}

Produces:

even numbers: [2, 4, 6, 8, 10]
doubles >>>>> [4, 8, 12, 16, 20]
the result is 60

Can I tee to a `logger`?

We can also log to a custom logger instance (slf4j) instead of stdout

(1..10)
    .filter { it % 2 == 0 }.teeToDebug(logger)
    .map { it * 2 }.teeToTrace(logger)
    .reduce(Int::plus).teeToInfo(logger) { "the result is $it" }