Gradle Tasks Difference

Question

What's the difference between the following two code snippets?

First:

task copyFiles(type: Copy) << {
  from "folder/from"
  into "dest/folder"
}

Second:

task copyFiles(type: Copy) {
  from "folder/from"
  into "dest/folder"
}

Answer 1

In short, the first snippet is getting it wrong, and the second one is getting it right.

A Gradle build proceeds in three phases: initialization, configuration, and execution. Methods like from and into configure a task, hence they need to be invoked in the configuration phase. However, << (which is a shortcut for doLast) adds a task action - it instructs the task what to do if and when it gets executed. In other words, the first snippet configures the task in the execution phase, and even worse, after its main (copy) action has been executed. Hence the configuration won't have any effect.

Typically, a task has either a type (which already brings along a task action) or a << (for an ad-hoc task). There are legitimate uses cases for having both (doing a bit of custom work after the task's "main" work), but more often that not, it's a mistake where the task gets configured too late.

I generally recommend to use doLast instead of <<, because it's less cryptic and makes it easier to spot such mistakes. (Once you understand the concepts, it's kind of obvious that task copyFiles(type: Copy) { doLast { from ... } } is wrong.)

Answer 2

The first block of code create a task and append an Action to it. A task is composed of actions which are instructions blocks run sequentially when the task is called

The second block create a task and configure it. These instructions are run in the gradle "configuration" lifecycle phase.

here you find a clear explanation of the differences

here you can find an in depth explanation of gradle tasks

here is the gradle guide about lifecycle