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" }

Produces:

[main] DEBUG ktee.KTeeTest - [2, 4, 6, 8, 10]
[main] TRACE ktee.KTeeTest - [4, 8, 12, 16, 20]
[main] INFO ktee.KTeeTest - the result is 60

This output was produced using slf4j-simple binding. Your output pattern may look different depending on logger's configuration

How do I add it to my project?

ktee is available in Maven Central 🎉

repositories {
    mavenCentral()
}

dependencies {
    implementation 'com.medly:ktee:1.0.0'
}