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I don't agree that C's NULL is any different from Java's null or modern C++'s nullptr, at least outside of embedded contexts (where sometimes people actually store stuff at the 0 address). Sure, it's normallt just a macro that resolves to 0 at the implementation level. But people use it like in C++: you want to return an int, but also distinguish the case where no int could be returned? Return an int*, and NULL signifies no data. > As for your question: something like 'keys(jsonobject).contains("fieldName")' ? Or 'NoSuchFieldException' thrown if you do 'jsonobject.get("fieldName")' ? > (The latter of which, given the general uneasiness NullPointerException creates in us devs, is often how a Java API will work anyway! Checked exceptions won the day! Until the Functional interface was made, at least.) I was thinking more of the case where you deserialize a JSON object into a Java object, and then inspect the Java object. Regardless, it was just an example - the problem of distinguishing "no value" from "any value" is pervasive in programming, and all languages must have some strategy for it. If we got rid of null from Java, then Option<T> would probably be the only general candidate. Which, to be fair, would be slightly better, as it would at least force you to check. > Or to answer it in the same spirit as this overall comment, why would you need to distinguish between missing and empty? Can't you just define the semantics of the document s.t. those two things having the same effect? Not in the general case, no. At least not without doubling every field and adding other inconsistency issues ({"result": "ABC", hasResult: false}). |