What's the design purpose of Gradle doFirst and doLast?

Question

For example I have the Gradle script like:

myTask_A {     doFirst {         println "first string"      }     doLast {         println "last string"     } } 

The following two tasks have exactly the same execution result:

myTask_B {     doFirst {         println "first string"         println "last string"     } }  myTask_C {     doLast {         println "first string"         println "last string"     } } 

What's the design purpose of the the doFirst & doLast as any of above tasks produces the same result?

Answer 1

It has to do with extensibility, reuse and avoiding duplication.

For one built in tasks can be extended like:

task CopyAndThen(type: Copy) {    doFirst {       println "this is before the actual copy"    }    doLast {       println "this is after the actual copy"    } } 

The second common scenario that comes to mind is with multi project builds, where you can have a task definition at the top of the project with common behavior:

allprojects {     task myTask_a {         doFirst {...}     } } 

And then the specific projects can extend that. The task essentially has a list of the Closures that needs to be run and the choice of doFirst or doLast controls to which end of the list the insert goes to.