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Let's say I had some function that takes a generic type as an argument. How do I check within that function whether the generic type argument is nullable or not? I want do something like this:
void func<T>() {
print(T is nullable);
}
void main(){
func<int>(); //prints false
func<int?>(); //prints true
}
All I can think of to do is to check if T.toString() ends with a ? which is very hacky.
816
Null-aware operators are used in almost every programming language to check whether the given variable value is Null. The keyword for Null in the programming language Dart is null. Null means a variable which has no values assign ever and the variable is initialized with nothing like.
Null Safety in simple words means a variable cannot contain a 'null' value unless you initialized with null to that variable. With null safety, all the runtime null-dereference errors will now be shown in compile time. String name = null ; // This means the variable name has a null value.
The Dart language now supports sound null safety! When you opt into null safety, types in your code are non-nullable by default, meaning that variables can't contain null unless you say they can.
Nullability and generics Like most modern statically-typed languages, Dart has generic classes and generic methods. They interact with nullability in a few ways that seem counter-intuitive but make sense once you think through the implications. First is that “is this type nullable?” is no longer a simple yes or no question.
Nullable types exist in the static type system, but the runtime representation of values uses the underlying type. If you have a “nullable 3”, at runtime it’s just the number 3. If you have an absent value of some nullable type, at runtime you just have the solitary magic value null. You can ask if a value is of a nullable type:
The null-aware operator is a nice tool for making nullable types usable in Dart. While we can’t let you call methods on nullable types, we can and do let you use null-aware operators on them. The post-null safety version of the program is:
Your Dart program has a whole universe of types in it: primitive types like intand String, collection types like List, and all of the classes and types you and the packages you use define. Before null safety, the static type system allowed the value nullto flow into expressions of any of those types.
Try:
bool isNullable<T>() => null is T;
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