4 ms·

this is called a bottom type in a type system. In JVM languages null and the throw expression return the bottom type. The only other option is to not have nil

this is called a bottom type in a type system. In JVM languages null and the throw expression return the bottom type. The only other option is to not have nil values.

kobeya 9y ago
Or to encapsulate a nil in a Maybe monad, so that you only have to deal with it in contexts where you explicity denote acceptance of nils. Then the type system won't let you get away with ignoring the possibility of a nil.
- deleted 9y ago
  [deleted]
- p4lindromica 9y ago
  you can do a maybe monad without nil types by substituting nil with a single-valued singleton type
junke 9y ago
The problem is "null" being a value in all (non primitive) types, not only the bottom type. You specify "String", but you can have "null" too. When everything is optional, how do you specify that function foo really takes a String, not null? (https://stackoverflow.com/questions/4963300/which-notnull-java-annotation-should-i-use?rq=1 https://stackoverflow.com/questions/4963300/which-notnull-ja...)
- mbel 9y ago
  > The problem is "null" being a value in all (non primitive) types, not only the bottom type. Null is not a value of bottom type. Bottom type has no values.
  - junke 9y ago
    Thanks, you are right, the bottom type has no value. I meant the "Null" type, which contains a single value, "null".
the8472 9y ago
> The only other option is to not have nil values. Rust has a bottom type (!)[0] without it implementing all traits by default while using a different type (Result) for error propagation. Plus having nil/null as a a value of the bottom type violates some aspects of bottomness. [0] https://github.com/rust-lang/rfcs/blob/master/text/1216-bang-type.md https://github.com/rust-lang/rfcs/blob/master/text/1216-bang...