Operator overloading or alternatives to expression templates

[Timon Gehr via Digitalmars-d]

On 09/11/2015 09:40 PM, Martin Nowak wrote:
> I find the reasons for turining down my ER a bit moot.
> ...

+1.

> [Issue 14593 – operator overloading can't be used with expression
> templates](https://issues.dlang.org/show_bug.cgi?id=14593)
>
> AFAIK expression templates are the primary choice tom implement SIMD and
> matrix libraries.

OTOH, they are a hack.

> And I still have [this idea](http://dpaste.dzfl.pl/cd375ac594cf) of
> implementing a nice query language for ORMs.
>
> D currently doesn't allow to override some operators like < <= > >= &&
> || !=.
>
> At least the comparison operators are really limiting, e.g. it's not
> possible to efficiently implement logical indexing.
>
> vec[vec < 15], vec[vec == 15], vec[(vec != 15) & (vec > 10)]
>
> Also opCmp is less efficient to implement than opBinary!"<" for many
> types. Generally any good implementation of an algorithm should only
> require a less operator, not a full ordering opCmp.
> ...

The rewrite a < b => a.opCmp(b)<0 is usually wasteful, but both methods 
can be the most efficient choice depending on the application. Two calls 
to opBinary!"<" will usually not be more efficient than one call to 
"opCmp".

I.e. the precedence should be the other way: try a.opBinary!"<"(b) first 
and then fall back to a.opCmp(b)<0. (Maybe it would also make sense to 
automatically provide opCmp if missing when opBinary!"<" has been 
implemented, such that generic code can use opCmp for all comparable 
types. Built-in comparable types should also provide opCmp.)

> The short circuit operators && and || have a special semantic and can't
> be easily, but there is & and | so it's not really required.
> ...

There's the 'lazy' keyword.

> ...
>
> Does anyone have a different idea how to make a nice query language?
> db.get!Person.where!(p => p.age > 21 && p.name == "Peter")
>

You could give up on operator syntax.