What is the difference between these task definiti

问题:

A)

task build << {  
  description = "Build task."  
  ant.echo('build')  
}

B)

task build {  
  description = "Build task."  
  ant.echo('build')  
}

I notice that with type B, the code within the task seems to be executed when typing gradle -t - ant echoes out 'build' even when just listing all the various available tasks. The description is also actually displayed with type B. However, with type A no code is executed when listing out the available tasks, and the description is not displayed when executing gradle -t. The docs don't seem to go into the difference between these two syntaxes (that I've found), only that you can define a task either way.

回答1:

The first syntax defines a task, and provides some code to be executed when the task executes. The second syntax defines a task, and provides some code to be executed straight away to configure the task. For example:

task build << { println 'this executes when build task is executed' }
task build { println 'this executes when the build script is executed' }

In fact, the first syntax is equivalent to:

task build { doLast { println 'this executes when build task is executed' } }

So, in your example above, for syntax A the description does not show up in gradle -t because the code which sets the description is not executed until the task executed, which does not happen when you run gradle -t.

For syntax B the code that does the ant.echo() is run for every invocation of gradle, including gradle -t

To provide both an action to execute and a description for the task you can do either of:

task build(description: 'some description') << { some code }
task build { description = 'some description'; doLast { some code } }