dealing with calling a java based fluent/builder a...

# getting-started

[Joe]

dealing with calling a java based fluent/builder api conditionally -- right now i've gotten to:

return Builder.builder().withIntParam(intParam).let {
     if (booleanFlag) {
           it.withBoolean()
     } else {
           it
     }
}.build()

anyone have a better pattern for something this? assuming the builder is mutable/side-effecty can change it to something like:

return ....apply {
   if (booleanFlag) { withBoolean() }
}

which is a little cleaner but might not work with all builder impls?

[Adam Powell]

Modifiers in Compose lend themselves to similar shapes; over there a utility like this ends up being useful:

inline fun <T> T.buildIf(condition: Boolean, builder: T.() -> T) = if (condition) builder() else this

then you end up with this at the call site:

Builder.builder()
  .withIntParam(intParam)
  .buildIf(booleanFlag) { withBoolean() }
  .build()

[Michael Böiers]

I’ve written this helpful little scope function which nicely encapsulates the if/else you need.

/**
 * returns the receiver if the condition doesn't hold, otherwise acts like a normal run
 */
public inline fun <T> T.runIf(condition: Boolean, block: T.() -> T): T = if (!condition) this else run(block)

with that you would just write

return Builder.builder()
  .withIntParam(intParam)
  .runIf(booleanFlag) { withBoolean() }
  .build()

[elizarov]

Cool use-case for https://youtrack.jetbrains.com/issue/KT-21477

[Joe]

Cool, any way to set up a contract (?) such that if condition is something like param != null then param is smart cast to non-nullable in the passed in lambda?