Add non-nullable reference types in C#
Non-nullability checks have to be manually encoded hundreds of times in any large real-world project, and they are not compile-time-enforced. There are code contracts in .Net 4.0, but their usage is still very verbose, and only partly compile-time-enforced.
What I wish is a pendant to the null-lifting operator ?, for instance, !, so that one could write:
void MyMethod(string! s){ /* s cannot be null :) */}
Or, the way ReSharper does it:
void MyMethod([NotNull] string s){ /* s cannot be null :) */}
Marc Sigrist
shared this idea
97 comments
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Marc Sigrist
commented
@Daniel Babralace: "Microsoft should really expand ? to be used for all types [...]" That's exactly what they will do in C# 8. See also https://github.com/dotnet/roslyn/blob/master/docs/Language%20Feature%20Status.md and https://github.com/dotnet/csharplang/blob/master/proposals/nullable-reference-types.md.
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Daniel Babralace
commented
Microsoft really missed a great opportunity when they introduced structs. Like the company often does, it fixated on the mechanics off programming rather than the concepts. Form follows function, and Microsoft often forgets the function when it gets tunnel vision on the form.
When Microsoft introduced structs, it added the ? syntax to mark structs as nullable since, being on the stack, structs couldn't be nullable without a new mechanism. And this is where Microsoft made two mistakes.
First, the application developer should not care at all whether something is on the stack or on the heap. The compiler, or better yet just-in-time compiler, should decide which is more efficient and just make a reference point to one or another. Thus there should be no keyword struct.
Second and even more importantly, Microsoft didn't have the foresight or the courage to make all references non-nullable unless explicitly opted in by the developer with the ? syntax. Yes, this would break backwards compatibility with existing source code, but it would have been worth it a million times over, especially since a simple app could easily restore backwards compatibility by appending ? to every reference to a non-atomic type. This would make migration to the new platform trivial.
Imagine if the compiler enforced that no variable and no parameter could be null unless declared with ?. Compile-time enforcement of non-null contracts would elimate countless problems and the declarations would be completely non-intrusive and obvioius. Let's just admit the real problem. Most programmers don't even think about null until a bug occurs. When most programers write
public String MyMethod (String p1, MyClass p2)
almost 100% of the time they really mean that the method does not take and does not return any nulls.
Let's say they did want to take nulls for p2, but not p1 and would not return nulls. See how much clearer the syntax is...
public String MyMethod (String p1, MyClass? p2)
And if they wanted to return nulls,
public String? MyMethod (String p1, MyClass p2)
Seeing String? as the return type would inform the caller that the method may return nulls and the programmer calling this method is more likely to actually think about the consequences of this.
Microsoft should really expand ? to be used for all types and make all references without ? to be non-nullable. A simple tool could translate source code to add ? to all references for backwards compatibility, and developers could then remove the unneeded ? at their leisure.
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Test
commented
test
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Muhammad El- Nakeep
commented
Here is the latest news: Introducing Nullable Reference Types in C#
: https://blogs.msdn.microsoft.com/dotnet/2017/11/15/nullable-reference-types-in-csharp/ -
Peter
commented
Maybe I'm oversimplifying things, but IMHO this could be done using an attribute to parameters:
void MyMethod([NotNull] string myParam)
{
}If the Compiler sees thiis, it injects something like
if (value == null)
{
throw new ArgumentNullException(nameof(value));
}Or even less verbs, by using something like the (string! myParam) the other poster proposed below.
And I also would like to see some simple null check. In C++ I can just werite
if (myPointer)
for null checks. In C# I always have to write
if (myRef == null)That's the only thing I don't like about C#: It is very verbose and needs a lot of code for simple things. Just look at Swift and how much less code it requires to express the same thing compared to C#.
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Roy T.
commented
It seems C#8 will bring this feature, though sort of in an opposite way. Adding warnings when an object can be null and allowing the ? operator on objects to signify that they can be null. See https://channel9.msdn.com/Blogs/Seth-Juarez/A-Preview-of-C-8-with-Mads-Torgersen (Nullable reference types)
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sjb
commented
I vote for it being a full-blown type. It would be a reference type, analogous to the fact that int? is a value type. So you would have nullable reference types and non-nullable reference types. Like this:
class BlogEntry {... }
public void Method( BlogEntry! r) { /* r != null is always true in the body */ }
...
BlogEntry myR;
...
BlogEntry! yourR = myR; // compile error, no implicit conversion from BlogEntry to BlogEntry!
BlogEntry! yourR = (BlogEntry!)myR; // compiles, run-time exception thrown if myR is null
...
myR = yourR; // compiles, implicit conversion from BlogEntry! to BlogEntry, no runtime exception.BlogEntry! hisR = new BlogEntry( ...) // compiles, hisR is definitely assigned
BlogEntry! hisR = yourR; // compiles, hisR is assigned same non-null value as yourRBlogEntry! goodExample( BlogEntry! someR) {
BlogEntry! hisR;
if (x == 7) {
hisR = new BlogEntry(...);
} else {
hisR = someR;
}
return hisR; // compiles, hisR is definitely assigned before use.
}BlogEntry! badExample( BlogEntry! someR) {
BlogEntry! hisR;
if (x == 7) {
hisR = someR;
}
return hisR; // compile error, hisR is not definitely assigned before use.
}BlogEntry!? otherR; // compile error, BlogEntry! is not a value type (also not legal syntax).
BlogEntry?! thirdR; // compile error, BlogEntry is not a value type (also not legal syntax)
int?! xx; // compile error, int? is not a reference type (also not legal syntax)
BlogEntry!! doubleR; // compile error, BlogEntry! is not a nullable reference type (also not legal syntax) -
.Net is failing
commented
Some interesting data from the 2017 Stack Overflow survey.
C# has fallen in popularity from 45% to 34% in just 5 years.
And Xamarin is one of the most dreaded technologies in the Stack Overflow survey.
The only really successful language Microsoft ever developed was classic VB, up to its best version ever - the VB6 programming language. They have never achieved the same success since.
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lindexi
commented
We use out that Do not know the scope.But we cant use not null.
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jaime weise
commented
how about creating something like using(...) { ... }* that null checks
with(someVariable) { ... }
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Jeroen Landheer
commented
What I do like would be using this for procedure parameters...
void MyMethod(someType! value){
/* s cannot be null, so no need for... */
if (value == null) throw new ArgumentNullException(nameof(value));}
This means the compiler simply inserts that null check code for us, so we won't have to write it all the time.
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commented
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Marc Sigrist
commented
I am happy to note that this suggestion has been at the very top ever since I wrote it more than five years ago. To understand its popularity, one can simply enter "billion dollar mistake" into any search engine.
Non-nullability is difficult to retrofit into a language like C#. There are many approaches, who solve the problem to varying degrees. Furthermore, the discussion is tricky, because people easily mix up the semantics of initialization, nullability, and optionality.
It is all the more exciting that non-null refs are now in the status of prototyping for the next version after C# 7 (see https://github.com/dotnet/roslyn/blob/master/docs/Language%20Feature%20Status.md).
Last not least: Several modern programming languages already _have_ null-avoidance features, such as F# (https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/values/null-values), Swift (https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/optional-type), or Rust (https://doc.rust-lang.org/std/option/).
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Marc Lewandowski
commented
This one is confused right from the title. OP doesn't want non-nullable reference *types*, he wants non-nullable *references*. Confusion throughout the discussion ensues.
Even that request is problematic: of what use is it? More to the point: are there sufficient cases where a conflict (null reference sent to non-null-reference param) could be detected at compile time to justify the addition of a new language feature?
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mgbrown commented
'"Add non-nullable reference types in C#" that would literally be a struct.'
Except that it wouldn't follow value semantics like a struct does. The referenced object would have a separate life time to its containing object. It could be shared between multiple referring objects.
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will motill
commented
This is basically suggesting that memory be allocated to a reference that potentially is just garbage data this actually would allow others to prevent you from doing a null check on it to find were a problem comes from how would this help anyone ?.
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will motill
commented
Btw "Add non-nullable reference types in C#" that would literally be a struct.
Seriously 4,082 votes to add a struct reference type to c# ?
Unless 4,082 voters really believe references other then struct's shouldn't need you the programmer to actually give them a value and should be non null if you forget to actually assign a non struct a value ?
Maybe what is supposed to happen is non structs should use magical energys to divine by supernatural process, Non null and non junk value. Getting these values from beyond the 10th dimension into the non struct Type reference which you forgot to define after declare it, in order to magically initialized it so dat its all ok now ????????<?>?<??...!?>?.