TxnDoubleCallable (Multiverse Core 0.7.0)

```
public interface TxnDoubleCallable
```
A transactional callable contains the logic that needs to be executed transactionally and normally is executed by the TxnExecutor. This transactional callable is optimized for retuning a primitive type: double. Using this TxnDoubleCallable instead of the TxnCallable is that no object wrapper needs to be created and there is no reason to deal with a potential null value.

Methods
Modifier and Type	Method and Description
`double`	`call(Txn txn)` Executes the callable.

Interface TxnDoubleCallable