Custom operator can't use external context

[vlalykin]

I register a new operation "LIKE":

public class MyExtension extends AbstractExtension {
    @Override
    public List<BinaryOperator> getBinaryOperators() {
        return Arrays.asList(
                new BinaryOperatorImpl("like", 20, LikeExpression.class, Associativity.LEFT)
        );
    }
}

I can only specify the class name LikeExpression. Its instance is created by the engine and there is no good way to inject some necessary data into the class instance. Filters have no such problem.

Now I see such context injection methods:

1. through a static variable of some class
2. through the context of template variables
3. when using spring extension - through SpringApplicationContext ("beans" variable). Similar to point (2), only the path to the goal is even longer

I suggest registering not a class, but a factory (or provider) of class instances:

LikeExpressionInstanceFactory factory = new LikeExpressionInstanceFactory( ... ); /* the desired context is passed here */
new BinaryOperatorImpl("like", 20, factory, Associativity.LEFT);

These two methods can exist together without breaking backward compatibility. Registering a class can use a lambda factory:

(clazz) -> clazz.newInstance ();

[vlalykin]

if you don't mind, I am ready to do PR

[ebussieres]

What data do you need to inject in LikeExpression class ?

[vlalykin]

cache instance for storing compiled regular expressions

[cjbrooks12]

I'd imagine this would improve performance slightly, too, as it would eliminate the need for reflection when evaluating operators

[ebussieres]

We can just change the BinaryOperatorImpl constructor. Instead of getting a

Class<? extends BinaryExpression<?>> nodeClass,

We should directly pass the instance of the class.

BinaryExpression<?> nodeClass,

We should do the same modification in UnaryOperatorImpl too

[vlalykin]

no, the parser every time creates a new instance of the class for each node in the tree

[vlalykin]

and initializes a new class (leftExpression, rightExpression, lineNumber)

[ebussieres]

My bad ... you're right

[vlalykin]

and the class itself is used as a marker to distinguish the filter expression and test expression from the rest of the expressions. I think this is not good.

it’s all easy to fix, you can pass the expression type to the constructor (for example, enum)

[vlalykin]

@ebussieres
Hi!
I created PR.
Have a look, please.

[vlalykin]

I used Java 8 syntax. Maybe I'm wrong? I did not find in the documentation whether pebble supports Java 7.
If compilation on Java 7 is required, let me know, please