A function declaration.

### Usage sample for toplevel function

Because some functions have type parameters, getting a model requires applying type arguments to the function declaration with `apply()` in order to be able to invoke that function. For example, here is how you would obtain a function model that you can invoke from a toplevel function declaration:

    String foo<T>(){
        return "Hello, our T is: ``typeLiteral<T>()``";
    }

    void test(){
        // We need to apply the Integer closed type to the foo declaration in order to get the foo<Integer> function model
        Function<String,[]> functionModel = `function foo`.apply<String,[]>(`Integer`);
        // This will print: Hello, our T is: ceylon.language::Integer
        print(functionModel());
    }

### Usage sample for methods

For methods it is a bit longer, because methods need to be applied not only their type arguments but also the containing type, so you should use `memberApply()` and start by giving the containing closed type:

    class Outer(){
        shared String hello() => "Hello";
    }

    void test(){
        // apply the containing closed type `Outer` to the method declaration `Outer.hello`
        Method<Outer,String,[]> methodModel = `function Outer.hello`.memberApply<Outer,String,[]>(`Outer`);
        // We now have a Method, which needs to be applied to a containing instance in order to become an
        // invokable function:
        Function<String,[]> boundMethodModel = methodModel(Outer());
        // This will print: Hello
        print(boundMethodModel());
    }

no type hierarchy

- `FunctionalDeclaration`
  - `GenericDeclaration`

- `FunctionalDeclaration`
  - `CallableConstructorDeclaration`
  - `FunctionDeclaration`

Attributes
`annotation` | Source Code `shared formal Boolean annotation` True if the current declaration is an annotation class or function.
`parameterDeclarations` | Source Code `shared formal FunctionOrValueDeclaration[] parameterDeclarations` The list of parameter declarations for this functional declaration.

Inherited Attributes
Attributes inherited from: `Object` `hash`, `string`
Attributes inherited from: `GenericDeclaration` `typeParameterDeclarations`

Methods
`apply` | Source Code `shared formal FunctionModel<Return,Arguments>&Applicable<Return,Arguments> apply<Return = Anything, Arguments = Nothing>(Type<Anything>[] typeArguments) given Arguments satisfies Anything[]` Applies the given closed type arguments to this function declaration in order to obtain a function model. See this code sample for an example on how to use this. Throws `IncompatibleTypeException` If the specified `Return` or `Arguments` type arguments are not compatible with the actual result. `TypeApplicationException` If the specified closed type argument values are not compatible with the actual result's type parameters.
`getParameterDeclaration` | Source Code `shared formal FunctionOrValueDeclaration? getParameterDeclaration(String name)` Gets a parameter declaration by name. Returns `null` if no such parameter exists.
`invoke` | Source Code `shared default Anything invoke(Type<Anything>[] typeArguments = [], Anything[] arguments)` Invokes the underlying toplevel function, by applying the specified type arguments and value arguments. Parameters: `typeArguments = []` Throws `IncompatibleTypeException` If the specified type or value arguments are not compatible with this toplevel function.
`memberApply` | Source Code `shared formal FunctionModel<Return,Arguments>&Qualified<FunctionModel<Return,Arguments>,Container> memberApply<Container = Nothing, Return = Anything, Arguments = Nothing>(Type<Object> containerType, Type<Anything>[] typeArguments) given Arguments satisfies Anything[]` Applies the given closed container type and type arguments to this method declaration in order to obtain a method model. See this code sample for an example on how to use this. Throws `IncompatibleTypeException` If the specified `Container`, `Return` or `Arguments` type arguments are not compatible with the actual result. `TypeApplicationException` If the specified closed container type or type argument values are not compatible with the actual result's container type or type parameters.
`memberInvoke` | Source Code `shared formal Anything memberInvoke(Object container, Type<Anything>[] typeArguments = [], Anything[] arguments)` Invokes the underlying method, by applying the specified type arguments and value arguments. Parameters: `typeArguments = []` Throws `IncompatibleTypeException` If the specified container, type or value arguments are not compatible with this method.

Inherited Methods
Methods inherited from: `Object` `equals()`
Methods inherited from: `GenericDeclaration` `getTypeParameterDeclaration()`