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13 Static Type Checking And Compilation - Reference Documentation

Authors: Graeme Rocher, Peter Ledbrook, Marc Palmer, Jeff Brown, Luke Daley, Burt Beckwith, Lari Hotari

Version: 3.0.2

13 Static Type Checking And Compilation

Groovy is a dynamic language and by default Groovy uses a dynamic dispatch mechanism to carry out method calls and property access. This dynamic dispatch mechanism provides a lot of flexibility and power to the language. For example, it is possible to dynamically add methods to classes at runtime and it is possible to dynamically replace existing methods at runtime. Features like these are important and provide a lot of power to the language. However, there are times when you may want to disable this dynamic dispatch in favor of a more static dispatch mechanism and Groovy provides a way to do that. The way to tell the Groovy compiler that a particular class should compiled statically is to mark the class with the groovy.transform.CompileStatic annotation as shown below.

import groovy.transform.CompileStatic

@CompileStatic class MyClass {

// this class will be statically compiled...

}

See these notes on Groovy static compilation for more details on how CompileStatic works and why you might want to use it.

One limitation of using CompileStatic is that when you use it you give up access to the power and flexibility offered by dynamic dispatch. For example, in Grails you would not be able to invoke a GORM dynamic finder from a class that is marked with CompileStatic because the compiler cannot verify that the dynamic finder method exists, because it doesn't exist at compile time. It may be that you want to take advantage of Groovy's static compilation benefits without giving up access to dynamic dispatch for Grails specific things like dynamic finders and this is where grails.compiler.GrailsCompileStatic comes in. GrailsCompileStatic behaves just like CompileStatic but is aware of certain Grails features and allows access to those specific features to be accessed dynamically.

13.1 The GrailsCompileStatic Annotation

GrailsCompileStatic

The GrailsCompileStatic annotation may be applied to a class or methods within a class.

import grails.compiler.GrailsCompileStatic

@GrailsCompileStatic class SomeClass {

// all of the code in this class will be statically compiled

def methodOne() { // … }

def methodTwo() { // … }

def methodThree() { // … } }

import grails.compiler.GrailsCompileStatic

class SomeClass {

// methodOne and methodThree will be statically compiled // methodTwo will be dynamically compiled

@GrailsCompileStatic def methodOne() { // … }

def methodTwo() { // … }

@GrailsCompileStatic def methodThree() { // … } }

It is possible to mark a class with GrailsCompileStatic and exclude specific methods by marking them with GrailsCompileStatic and specifying that the type checking should be skipped for that particular method as shown below.

import grails.compiler.GrailsCompileStatic
import groovy.transform.TypeCheckingMode

@GrailsCompileStatic class SomeClass {

// methodOne and methodThree will be statically compiled // methodTwo will be dynamically compiled

def methodOne() { // … }

@GrailsCompileStatic(TypeCheckingMode.SKIP) def methodTwo() { // … }

def methodThree() { // … } }

Code that is marked with GrailsCompileStatic will all be statically compiled except for Grails specific interactions that cannot be statically compiled but that GrailsCompileStatic can identify as permissible for dynamic dispatch. These include things like invoking dynamic finders and DSL code in configuration blocks like constraints and mapping closures in domain classes.

Care must be taken when deciding to statically compile code. There are benefits associated with static compilation but in order to take advantage of those benefits you are giving up the power and flexibility of dynamic dispatch. For example if code is statically compiled it cannot take advantage of runtime metaprogramming enhancements which may be provided by plugins.

13.2 The GrailsTypeChecked Annotation

GrailsTypeChecked

The grails.compiler.GrailsTypeChecked annotation works a lot like the GrailsCompileStatic annotation except that it only enables static type checking, not static compilation. This affords compile time feedback for expressions which cannot be validated statically at compile time while still leaving dynamic dispatch in place for the class.

import grails.compiler.GrailsTypeChecked

@GrailsTypeChecked class SomeClass {

// all of the code in this class will be statically type // checked and will be dynamically dispatched at runtime

def methodOne() { // … }

def methodTwo() { // … }

def methodThree() { // … } }