driver-core/src/main/com/mongodb/client/model/Projections.java
public static <TExpression> Bson computed(final String fieldName, final TExpression expression) {
        return new SimpleExpression<TExpression>(fieldName, expression);
    }
public static <TExpression> Bson computed(final String fieldName, final TExpression expression) {
        return new SimpleExpression<TExpression>(fieldName, expression);
    }
Creates a projection of a field whose value is computed from the given expression.  Projection with an expression is only supported
using the $project aggregation pipeline stage.

@param fieldName     the field name
@param expression    the expression
@param <TExpression> the expression type
@return the projection
@see Aggregates#project(Bson)