non-nullable | 易学教程

Create Non-Nullable Types in C#

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How to create non-nullable value types like int, bool, etc. in C#? Yes, these are called struct . Structs are value types, just like int , bool and others. They have some rules/recommendations related to them: (I think these are the most important) a struct is passed and assigned by value, when not using ref or out keywords... this means that everything you put inside a struct will be copied when assigning or passing it to a method. That is why you should not make large structs. you cannot define a parameterless constructor for a struct in C# structs are better to be immutable, and have no

How can I get close to non-nullable reference types in C# today?

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I've read many of the non-nullable questions and answers. It looks like the best way to get close to non-nullable types in C# (4.0) is Jon Skeet's NonNullable<> hack. However, it seems that C++/CLI has solved much of the problem by supporting managed references: Foo% (instead of native C++ Foo& ). The compiler makes this work by adding modreq(IsImplicitlyDereferenced) to the argument. Trying to call such a function from C# results in: '<FunctionName>' is not supported by the language Is there anything better then NonNullable<> ? Is there any way to (reasonably--i.e., w/o using reflection) call

Why @Nonnull annotation checked at runtime?

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I have a function with following signature public static String myFunction(@Nonnull String param) When I call it with param as null, I get the following exception: Caused by: java.lang.IllegalArgumentException: Argument for @Nonnull parameter 'param' of com/MyClass.myFunction must not be null at com.MyClass.$$$reportNull$$$0(MyClass.java) javax.annotation.Nonnull supposed not to be checked at runtime. Who actually throws the exception and why? P.S. I run Tomcat server in debug mode from IntelliJ IDEA 2016.3 with Oracle JDK 1.8.0_102 When you compile your project in IntelliJ IDEA, it

IntelliJ IDEA @ParametersAreNonnullByDefault for all subpackages

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问题 I use IntelliJ's null-checking mechanism to prevent nullpointer crashes. I've successfully set up all Java method parameters to be @NonNull by default using this answer. After creating package-info.java which is used to define package annotations in Java. All java files which are direct descendants of that package have methods with default @NonNull parameters in my Android Studio project. The obvious problem is that I need to define @ParametersAreNonnullByDefault for all Java classes in that

Value of unassigned non-nullable variable (C#)

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问题 Just curious. If you go: string myString; Its value is null. But if you go: int myInt; What is the value of this variable in C#? Thanks David 回答1: Firstly, note that this is only applicable for fields, not local variables - those can't be read until they've been assigned, at least within C#. In fact the CLR initializes stack frames to 0 if you have an appropriate flag set - which I believe it is by default. It's rarely observable though - you have to go through some grotty hacks. The default

Create Non-Nullable Types in C#

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问题 How to create non-nullable value types like int, bool, etc. in C#? 回答1: Yes, these are called struct . Structs are value types, just like int , bool and others. They have some rules/recommendations related to them: (I think these are the most important) a struct is passed and assigned by value, when not using ref or out keywords... this means that everything you put inside a struct will be copied when assigning or passing it to a method. That is why you should not make large structs. you

Best explanation for languages without null

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Every so often when programmers are complaining about null errors/exceptions someone asks what we do without null. I have some basic idea of the coolness of option types, but I don't have the knowledge or languages skill to best express it. What is a great explanation of the following written in a way approachable to the average programmer that we could point that person towards? The undesirability of having references/pointers be nullable by default How option types work including strategies to ease checking null cases such as pattern matching and monadic comprehensions Alternative solution

In Kotlin, what is the idiomatic way to deal with nullable values, referencing or converting them

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问题 If I have a nullable type Xyz? , I want to reference it or convert it to a non-nullable type Xyz . What is the idiomatic way of doing so in Kotlin? For example, this code is in error: val something: Xyz? = createPossiblyNullXyz() something.foo() // Error: \"Only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type Xyz?\" But if I check null first it is allowed, why? val something: Xyz? = createPossiblyNullXyz() if (something != null) { something.foo() } How do