Operator overloading or alternatives to expression templates

[Sebastiaan Koppe via Digitalmars-d]

On Friday, 11 September 2015 at 19:41:41 UTC, Martin Nowak wrote:
> Does anyone have a different idea how to make a nice query 
> language? db.get!Person.where!(p => p.age > 21 && p.name == 
> "Peter")

In our last project we took the following approach:

`auto q = query.builder!Person.age!">"(20).name("Peter");`

In the query-builders there was a lot of ugly concatenating sql 
stuff. But there was just one guy writing that, everybody else 
was using the high-level functions.

It allows for a lot of checking, not only on types but also on 
logic (e.g. age!">"(20).age!"<"(10) was caught at runtime). Plus, 
very unittestable.

It worked so well that once the query-builders were written, all 
the constraints, sorting and ordering parameters could be passed 
straight from the http api down to the query-builders.

Still, you would have to write the query-builders for each Object 
you want query, although that is something you could do in a DSL.