non-nullable

问题 I get a warning from eclipse and I know I can remove it with suppress warning but I'd prefer to understand what makes it thing it could be null. package-info.java @ParametersAreNonnullByDefault package test; import javax.annotation.ParametersAreNonnullByDefault; test.java package test; public class Test { public static void main( final String[ ] args ) { System.out.println( new Test( "a" ).getS( ) ); } private final String s; public Test( final String s ) { this.s = s; } public String getS( )

问题 I once read that having nullable types is an absolute evil. I believe it was in an article written by the very person who created them(in Ada?) I believe this is the article Anyway, so what if by default a language like C# used non-nullable types? How would you replace some of the common idioms in C# or Ruby or any other common language where null is an acceptable value? 回答1: Instead of outright declaring that nullable types are evil, I would posit: most languages graft nullability onto

问题 Why it is not allowed to assign null to a DateTime in C#? How has this been implemented? And can this feature be used to make your own classes non-nullable? Example: string stringTest = null; // Okay DateTime dateTimeTest = null; // Compile error I know that I can use DateTime? in C# 2.0 to allow null to be assigned to dateTimeTest and that I could use Jon Skeet's NonNullable class on my string to get a run time error on the assignment of stringTest. I'm just wondering why the two types

问题 I'm designing a language, and I'm wondering if it's reasonable to make reference types non-nullable by default, and use "?" for nullable value and reference types. Are there any problems with this? What would you do about this: class Foo { Bar? b; Bar b2; Foo() { b.DoSomething(); //valid, but will cause exception b2.DoSomething(); //? } } 回答1: My current language design philosophy is that nullability should be something a programmer is forced to ask for, not given by default on reference

问题 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

问题 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

问题 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

问题 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

问题 I want to implement a generic function in Java8, that verifies that a collection has no null members and returns a type with @NonNull annotation. input type: T extends Collection, where T+U are nullable. result type: @NonNull T, with @NonNull U For array this would look like this: public static <T> @NonNull T @NonNull[] arrayHasNoNullMember( @Nullable T @Nullable[] value) { But for the collection case, i don't know how to define that the result type is the same as the input type, but has the

问题 Using Entity Framework version 4.0 (or any other version that is compatible with .NET 4.0), I want to map this existing relational database schema: to this logical object model: which I have tried setting up as follows: (I hope the German captions won't be too disorienting.) Entity Framework gives me this error: Error 3031: Problem in mapping fragments …: Non-nullable column FooBs.B in table FooBs is mapped to a nullable entity property. In the logical model, B ought to be nullable. However,