object DefaultHelper
A helper containing the sealed DefaultsTo
trait which is used to determine the default type for a given method.
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sealed
class
DefaultsTo
[A, B] extends AnyRef
Neat helper to obtain a default type should one not be given eg:
Neat helper to obtain a default type should one not be given eg:
def find[T]()(implicit e: T DefaultsTo Document) { ... }
The signature of the
find
method ensures that it can only be called if the caller can supply an object of typeDefaultsTo[T, Document]
. Of course, the DefaultsTo.default andDefaultsTo.overrideDefault methods make it easy to create such an object for any type
T. Since these methods are implicit, the compiler automatically handles the business of calling one of them and passing the result into
find.
But how does the compiler know which method to call? It uses its type inference and implicit resolution rules to determine the appropriate method. There are three cases to consider:
1.
find
is called with no type parameter. In this case, type T must be inferred. Searching for an implicit method that can provide an object of typeDefaultsTo[T, Document]
, the compiler findsdefault
andoverrideDefault
.default
is chosen since it has priority (because it's defined in a proper subclass of the trait that defines overrideDefault). As a result, T must be bound toDocument.
2.
find
is called with a non-Document type parameter (e.g.,find[BsonDocument]()
). In this case, an object of typeDefaultsTo[BsonDocument, Document]
must be supplied. Only theoverrideDefault
method can supply it, so the compiler inserts the appropriate call.3.
find
is called withDocument
as the type parameter. Again, either method is applicable, but default wins due to its higher priority. -
trait
LowPriorityDefaultsTo
extends AnyRef
Lower priority defaultsTo implicit helper
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object
DefaultsTo
extends LowPriorityDefaultsTo
Companion object for DefaultsTo
This is the documentation for the MongoDB Scala driver.
Driver structure
The mongodb scala driver.
To get started you need a MongoClient instance, either from a connection string or via a org.mongodb.scala.MongoClientSettings.
Notable packages include: