Is it possible to collect object usage information during compilation?

[Martin Nowak via Digitalmars-d]

On 01/10/2015 11:20 AM, Jacob Carlborg wrote:
> On 2015-01-10 07:46, DaveG wrote:
>> I might be crazy, but it seems like the compiler has all the information
>> necessary to figure this out and it would make user code simpler, less
>> error prone, and more efficient. So does anybody have any idea on how to
>> actually achieve this?
>
> I'm not exactly sure if this is what you want but you can implement the
> "opDispatch" [1] method in a class or struct. This method will be called
> if no other method exists with the same name. There's also something
> called "alias this" [2] that allows you to do something similar.
>
> class Foo
> {
>      void foo () {}
>      void opDispatch (string name)() {}
> }
>
> auto f = new Foo;
> f.foo(); // will call "foo"
> f.bar(); // will be lowered to f.opDispatch!("bar")();
>
> If you're implementing an ORM I would recommend executing queries
> lazily. You can do something like this:
>
> class Person : ORM.Base
> {
>      String name;
>      Int age;
>
> // this method returns a range/proxy that implements the range api [3]
>      static ORM.Range!(Person) all () {}
> }
>
> "String" would look something like this:
>
> struct String
> {
>      alias get this;
>
>      // this method will fetch the data from the database
>      private string get ();
> }
>
> Using the interface would look something like this:
>
> auto p = Person.all(); // no database query has been performed yet
>
> // the range interface makes it possible to use a foreach
> // when starting the foreach loop is when the first query will happen
> foreach (e ; p)
> {
>      // this call will trigger a call to the "get" method in "String"
>      // via the "alias this"
>      string name = e.name;
>      writeln(name);
> }

The idea isn't bad, but the performance will suck. This is generally 
known as N+1 query, only that this is even worse, as each field is 
queried individually.

Here is a sketch for an optimal solution. I'm actually eagerly waiting 
that someone finally implements it.

http://dpaste.dzfl.pl/cd375ac594cf