Notice: This Wiki is now read only and edits are no longer possible. Please see: https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/wikis/Wiki-shutdown-plan for the plan.
RoadmapOAW5
Contents
Collection of features (rough)In Version 5 we want to improve some of the Xtend language concepts and features. Codename is Xtend++ : ImportsThe import mechanism should be overworked, so that every import is explicite. We won't need any metamodel configuration in the workflow nor in the editors anymore. This will not only make the setup simpler but will also improve the performance. The syntax would change to something like the following: import org:openarchitectureware:Extension; // native import import EMF "my/package/model.ecore"; // non-native import import UML "my/test.profile.uml" as profile; // non-native import with name space definition import Java "my.test.Class"; // non-native import introduces java types and features form my.test.Class import XSD "http://www.mywebsite.org/xsd/metamodel.xsd" // non-native import importing the types from an XSD file ... (think of Hibernate mapping files, Groovy, etc.) Native importA native import refers to another extension file imports all public members (types, functions, extensions). Non-native ImportA non native import starts with an identifier pointing to an installed adapter. The adapter is responsible for loading and converting the type information from the given string. The syntax in the string is defined by the adapter. Namespace definitionAll members are included without namespace information. If you need a namespace you can explicitely define one per import. ReexportThe reexport keyword will be supported. GenericsWe need full-fledged generics, which can conceptually be copied from Java's generics. Maybe we can leave out some of the more advanced capabilities? ClosuresWe'll have real closures, not the built-in stuff we have now. Closure syntax: parameterList '|' expression-using-parameters-and-scope Where parameter list must be typed, either implicit or explicit. Example: // type of e is inferred from the declaration of the 'select()' function myList.select(e|e.name == "test") or { String myText := "test"; (Attribute)=>Boolean myClosure := e|e.name==myText; // e is inferred from the declared type of the assignee myList.select(myClosure); } alternatively declare the parameter types explicitly { var myText := "test"; var myClosure := Attribute e|e.name==myText; myList.select(myClosure); }
Declaring Closure typesThe syntax for of a closure type is (parameterTypes)=>returnType Examples: ()=>Object (String)=>Boolean (String, Entity)=Entity Example 2: declaration of higher-order functions using generics : List<T> select<T>(List<T> this, (T)=>Boolean closure) { ... } Extensions/FunctionsIn the first version there will only be functions (aka. extensions). Functions can be invoked either using the functional syntax or using the member syntax (operation like): myFunction(foo, bar) == foo.myFuntion(bar) A function is declared as follows: (private|cached) ReturnType? functionName(declaredParameterList) guardExpression? : bodyExpression ; Example: private doStuff(Entity this) name!=null : name+"Stuff"; or (private|cached) functionName(declaredParameterList) guardExpression blockExpression Example: cached makeAbstract(Entity this) { abstract := true; name := 'Abstract'+name; return this; } Polymorphic GuardsThe guards are used for polymorhpic resolution of a called extension. Example: context Entity { String javaName() isAbstract : "Abstract"+name; String javaName() : name; } The dynamic semantics are:
The static semantics are straight forward: The guard must be of type boolean. Code blocksA code block is the replacement for chain expressions ( a-> b-> x) with the additional features:
It's something like a pseudo imperative syntax (but still is an expression!). Example: myExtension(String stuff) { var x := stuff.length(); if (x>56) return "Foo"; else { return "Bar"; } } A code block is itself an expression consisting of a list of expressions. It returns the value returned by the first executed "return-expression", or the value of the last expression. It is possible to overwrite the scope. Example: doStuff() { var x := "Foo"; { var x:= "Bar"; return x; } } will return "Bar" Object creation expressionWe are thinking about a syntax to create model graphs inline. We need this not only for model transformations but also for writing model transformation tests. Example: new Entity { name := "Person"; references += new Reference { name := "someRef" type := anotherEntity } } Assignment ExpressionsThey are just another syntax for invoking a setter resp. adder-operation (which will be removed). They return the assigned value. create / cache semanticsThe creation expression should replace the "create extension" mechanism from Xtend 1.0. A creation of an Object is cached if the type name is suffixed with parenthesis containing any number of arguments. The arguments act as a key. Examples: var paramPerOperationAndName := new Parameter(op,name) { this.name := name; type := aDatatype; } var localSingleton := new Foo() { stuff := "bla"; } cross referencingWe need a way to specify cross references within a declared tree. The problem is that we need a reference to a created type after it has been created and before it will be initialized. This can be accomplished by adding a special assignment construct: var x := new localRef:=Entity { // x is not visible here, because the right hand expression has not been evaluated so far. // localRef holds a reference to the created but not yet initialized entity. name := "Person"; references += new Reference { name := "partner" type := localRef } }
if expressionAs seen in the previous example, we want an if-expression. using if, else keywords. if (predicate) expression (else if (predicate) expression)* (else expression)? The else part is optional and will return null if not defined. The following expression will return null: if (false) "Holla" Integration of CheckThe language check will be integrated into Xtend. That is you can define checks and extensions in the same file: allEntities(emf::EObject obj) : eRootContainer.eAllContents.typeSelect(Entity); context Entity { warning "name "+name+" should start with an uppercase letter" : name.firstToLowerCase()!=name error "duplicate name "+name : allEntities(this).select(e|e.name==name).size==1; } of course you can use everything we have defined before in checks, too. Example :
context Entity { error "duplicate name "+name { var entities := eRootContainer.eAllContents.typeSelect(Entity); allEntities(this).select(e|e.name==name).size==1; } Definition of TypesSo far we couldn't define Types within Xtend but had to define them using other techniques (ecore, Java, UML-profile, etc.). Defining tyoes within Xtend would be a great feature. Because it is much simpler and faster to write them in text. In addition we could define Type with logic (operations). A syntax could look like this: type Entity extends Named { // simple attributes String name; Boolean isAbstract { private set(aValue) get : name.startsWith("Abstract"); }; // references Set<Entity> superTypes; Set<Features>* features; // asterisk means containment Set<Reference>* references subsets features; // operations doStuff(String x) : x+name; doMoreStuff(String x) { name := x; features += var f := new Feature{ f.name:= x; ... }; } } Template syntaxWe want to come up with a simple template syntax integrated into Xtend. Example: context Entity { toJava() : »package «packageName()»; public class «name» { «attributes.each(a|» public «a.type» «a.name»; «)» }«; It's just a string literal with the xpand terminals '«' and '»'. In addition if you use these type of string literals, string concatenation is implicit. Under the hood we might come up with a special string type (for performance reasons), but it should be compatible to the oaw String type and therefore transparent to the user. Files are opened thorugh extensions:
generateCode(Entity e) : writeToFile(e.JavaFile(),e.toJava());
Extensions overwrite semanticsExtensions with the same signature will overwrite Operations. Consider overwriting the toString() Operation (which is invoked on String concatenations) for arbitrary meta types. This will allow very readable templates.
Optional parentheses for operations, functions, extensions without parametersWe should discuss if we want to make empty parentheses on invocations of operations optional. So that : my.operation() equals my.operation
Xpand ContainerWe'll have a possibility to add a string to a previously defined "outlet" |