I'm not sure of the best channel for this discussion, but it deals with delegates and how they are u...

# announcements

[ciscorucinski]

I'm not sure of the best channel for this discussion, but it deals with delegates and how they are used to grab Property File values.

I have seen it described very similarly before in an article that we can use a simple convention such as

val pluginGroup: String by project

This will search for .property files for the key pluginGroup and return it's value as a String . I am impressed by that, but how the heck does this magic work?

This will only return String values, so even if we have the following in the .properties file...

platformDownloadSources = true

It will still only return "true" as a String .

I am curious of how this mechanism works and why it is limited to only String and why it is limited to the specific name I have for the variable. Meaning I must name my variable the same as is in the .properties file.

[Vampire]

Properties implements Map so this applies: https://kotlinlang.org/docs/reference/delegated-properties.html#storing-properties-in-a-map

[ciscorucinski]

To see this in usage, head over to GitHub: JetBrains/intellij-platform-plugin-template

Here is gradle.properties and here is build.gradle.kts

[Vampire]

Ah, you're talking about Gradle project, but well, it is similar. The Kotlin DSL seems to provide the respective methods for property delegation to work.

[ephemient]

#C19FD9681 or https://gradle-community.slack.com/ might have more details

[ephemient]

but yeah, https://github.com/gradle/gradle/blob/master/subprojects/kotlin-dsl/src/main/kotlin/org/gradle/kotlin/dsl/ExtensionContainerExtensions.kt defines getValue() on ExtensionContainer (which Project is)

[ephemient]

there's a few other types and extensions so that by extra, by ext(defaultValue) etc work

[ephemient]

as for how Gradle's extensions work, that's another story altogether

[ciscorucinski]

ah, so this might be more of a Gradle specific question that uses Kotlin rather than the other way around.

[Vampire]

Exactly