DIP 50 - AST macros

[luka8088]

On 13.11.2013. 9:26, Jacob Carlborg wrote:
> On 2013-11-12 17:14, John Colvin wrote:
> 
>> oh, I see. Would AST macros really be enough to make this work in D?
>> "Arbitrary code" is a huge feature space in D, including much that
>> doesn't map well to anything outside of a relatively low-level language,
>> let alone SQL.
>> I can see it quickly becoming a nightmare that would be worse than just
>> issuing the predicate as an sql string or some generic equivalent.
> 
> Person.where(e => e.name == "John")
> 
> I'm thinking that we only need to convert the part that is prefixed
> with, in this example, "e". Any other code should be executed in the
> context of the caller. It should be possible to do this as well:
> 
> auto foo = "John";
> auto result = Person.where(e => e.name == foo);
> 
> Which will result in the same SQL query.
> 
> I'm using a pluign to Ruby on Rails that does something similar but by
> overloading operators. The problem with this approach, in Ruby, is that
> you cannot overload operators like || and &&, so instead they overload |
> and & resulting in new problems like operator precedence. Example:
> 
> Person.where{ |e| (e.name == "John") & (e.address == "Main street") }
> 

What about something like this?

class Person {

  macro where (Context context, Statement statement) {
    // ...
  }

}

auto foo = "John";
auto result = Person.where(e => e.name == foo);

// is replaced by
auto foo = "John";
auto result = Person.query("select * from person where person.name = " ~
sqlQuote(foo) ~ ";");