(Quick Reference) # 14 Static Type Checking And Compilation Version: 6.0.0 ## Table of Contents # 14 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. ## 14.1 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. ## 14.2 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() {
            // ...
        }
    }
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