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MongoIterable.forEach requires a Block which is very similar to Java 8 Consumer. They are similar enough to cause problems, for example, the following doesn't compile:

MongoIterable<Document> result = collection.find(...);
result.forEach(System.out::println);

because the compiler can't decide between Iterable.forEach( Consumer ) and MongoIterable.forEach( Block ). Fixing this requires workarounds like explicitly typing the parameter:

Block<Document> printer = System.out::println;
result.forEach(printer);

or alternatively, treating MongoIterable as a plain Stream:

StreamSupport.stream(result.spliterator(), false).forEach(System.out::println);

Why is MongoIterable.forEach not defined using the Consumer interface, something like: MongoIterable.forEach(Consumer<? super TResult> consumer)? Even better - why have forEach in MongoIterable at all?

David Soroko
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1 Answers1

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The Java driver still supports Java 6 as a target. So while the attempts were made to make the 3.0 driver Java 8 and lambda friendly, we couldn't use actual Java 8 interfaces.

evanchooly
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  • This explains why Consumer is not used, but I am still not clear as to why have MongoIterable.forEach in the first place. Is it to give non Java 8 users a Java 8 like experience ? – David Soroko Jan 08 '16 at 09:23
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    It was intended to make it more friendly. The jury's still out if that goal was achieved or not. – evanchooly Jan 10 '16 at 21:52
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    It would have been nice to have a different name to avoid the name class, like `forEachMongo` (or maybe an even cooler name?). Luckily a simple type cast solves the issue. – Freek de Bruijn Nov 05 '16 at 21:13