4 ms·

NULL exists in every programming language. There must be something to designate a missing value, a non assigned pointer or reference.

ancarda 8y ago
Most languages, sure, but not all; Haskell doesn’t have NULL. You can express the absense of a value with a Maybe: Just “value” -> Maybe String Nothing -> Maybe a If your function returns a “Maybe String”, it can either be just a value, or Nothing. However, if a function returns a “String”, you can’t return Nothing, only an actual String. There’s no null in Haskell.
baq 8y ago
yeah... no. most notably rust, which might be surprising as it can be used (and has been) to write a kernel in, only has null pointers in unsafe code. rust is hardly the first one, too.
masklinn 8y ago
> NULL exists in every programming language. No. > There must be something to designate a missing value, a non assigned pointer or reference Option types are something like 45 years old, they're not exactly futuristic technology.
antonvs 8y ago
There has to be a way to represent a missing value, but the key point in languages that don't have NULL is that you can only represent missing values using a type that supports missing values - e.g. option types such as Haskell's Maybe. This achieves two things: 1. It allows you to define functions that cannot return NULL, and the compiler guarantees this. This is a huge win - you no longer have NULL as a possible return value for many functions. 2. Values belonging to the option type have to be unwrapped to access their contents, so it's not possible to unknowingly dereference a missing value. This is an even bigger win than #1, because it can literally eliminate null pointer errors. A caveat to #2 is that depending on the language, it may be possible to override safety, for example Haskell's fromJust can throw an exception if used on a missing value. But this tends to require conscious effort, and can easily be checked for automatically, since it involves the use of unsafe function calls.
- masklinn 8y ago
  > A caveat to #2 is that depending on the language, it may be possible to override safety, for example Haskell's fromJust can throw an exception if used on a missing value. But this tends to require conscious effort, and can easily be checked for automatically, since it involves the use of unsafe function calls. A much scarier example there is C++, where std::optional can be deref'd (literally `*opt`, the easiest and shortest thing you can do with it)… and just UBs on an empty optional. Because C++ hates both type-safety and memory-safety.

ancarda 8y ago

Most languages, sure, but not all; Haskell doesn’t have NULL. You can express the absense of a value with a Maybe: Just “value” -> Maybe String Nothing -> Maybe a If your function returns a “Maybe String”, it can either be just a value, or Nothing. However, if a function returns a “String”, you can’t return Nothing, only an actual String. There’s no null in Haskell.

baq 8y ago

yeah... no. most notably rust, which might be surprising as it can be used (and has been) to write a kernel in, only has null pointers in unsafe code. rust is hardly the first one, too.

masklinn 8y ago

> NULL exists in every programming language. No. > There must be something to designate a missing value, a non assigned pointer or reference Option types are something like 45 years old, they're not exactly futuristic technology.

antonvs 8y ago

There has to be a way to represent a missing value, but the key point in languages that don't have NULL is that you can only represent missing values using a type that supports missing values - e.g. option types such as Haskell's Maybe. This achieves two things: 1. It allows you to define functions that cannot return NULL, and the compiler guarantees this. This is a huge win - you no longer have NULL as a possible return value for many functions. 2. Values belonging to the option type have to be unwrapped to access their contents, so it's not possible to unknowingly dereference a missing value. This is an even bigger win than #1, because it can literally eliminate null pointer errors. A caveat to #2 is that depending on the language, it may be possible to override safety, for example Haskell's fromJust can throw an exception if used on a missing value. But this tends to require conscious effort, and can easily be checked for automatically, since it involves the use of unsafe function calls.

masklinn 8y ago
> A caveat to #2 is that depending on the language, it may be possible to override safety, for example Haskell's fromJust can throw an exception if used on a missing value. But this tends to require conscious effort, and can easily be checked for automatically, since it involves the use of unsafe function calls. A much scarier example there is C++, where std::optional can be deref'd (literally `*opt`, the easiest and shortest thing you can do with it)… and just UBs on an empty optional. Because C++ hates both type-safety and memory-safety.