CODEWITHSUNDEEP
metaprogrammingceylon
user3464741
user3464741

Reputation:

Runtime meta programming in ceylon

I get unexpected results from the following code snippet using the eclipse ide:

class Example(String s = "init") {
    shared String a() => "Func 1";
    shared String b = "Attr 1";
    shared String c(Integer i) { return "Func 2"; }
}


shared
void run() {    

  // 1.
  print("getAttributes: " + `Example`.getAttributes().string);
  print("getMethods:    " + `Example`.getMethods().string);
  // prints:   []  
  // i.e. doesnt print any attribute or method

  // 2.
  value e = Example()
  type(e);  // error
  e.type(); // error, should be replaced by the ide with the above version.

}

ad 1.) I get as a result:

getAttributes: []
getMethods:    []

where I expected lists containing attributes or methods.

ad 2.) The doc says:

"The type() function will return the closed type of the given instance, which can only be a ClassModel since only classes can be instantiated. ..."

But I cant find the type() function and others related to meta programming, i.e. I dont get a tooltip, but instead I get a runtime (!) error:

Exception in thread "main" com.redhat.ceylon.compiler.java.language.UnresolvedCompilationError: method or attribute does not exist: 'type' in type 'Example'

So, where is the equivalent to the backticks `Example`.... as a function ?

Upvotes: 1

Views: 102

Answers (1)

Lucas Werkmeister
Lucas Werkmeister

Reputation: 2742

  1. `Example`.getAttributes() returns an empty list because getAttributes takes three type arguments: Container, Get, Set. When called as getAttributes(), the typechecker tries to infer them, but since there’s no information (no arguments with the appropriate type), the inferred type argument is Nothing. Since Nothing is not a container of any of the class’ members, the resulting list is empty. Use getAttributes<>() instead to use the default type arguments, or specify them explicitly (e. g. getAttributes<Example>()). Same thing with getMethods(). Try online

  2. The type function is in ceylon.language.meta and needs to be imported: import ceylon.language.meta { type }. Once you do that (and remove the e.type() line), the compilation error will go away.

  3. If you directly want a meta object of the function, you can write `Example.a`.

Upvotes: 0

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