I first tought your question was a dupe of What code does the compiler generate for autoboxing? However, after your comment on @ElliottFrisch I realized it was different : I know the compiler behaves that way. I’m trying to figure out whether that behavior is guaranteed. For other readers, assume that “behaves that way” means … Read more
Finding the most specific method is defined in a very formal way in the Java Language Specificaion (JLS). I have extracted below the main items that apply while trying to remove the formal formulae as much as possible. In summary the main items that apply to your questions are: JLS 15.12.2: your use case falls … Read more
Boxing refers to a conversion of a non-nullable-value type into a reference type or the conversion of a value type to some interface that it implements (say int to IComparable<int>). Further, the conversion of an underlying value type to a nullable type is also a boxing conversion. (Caveat: Most discussions of this subject will ignore … Read more
There are two things going on: 1) The compiler treats “null” not as a null reference but as a null value… the null value for whatever type it needs to convert to. In the case of a Nullable<T> it’s just the value which has False for the HasValue field/property. So if you have a variable … Read more
If you need different behaviour when you’re dealing with a value-type then you’re obviously going to need to perform some kind of test. You don’t need an explicit check for boxed value-types, since all value-types will be boxed** due to the parameter being typed as object. This code should meet your stated criteria: If value … Read more
Jon’s point is true, but as a side note there is one slight exception to the rule; generics. If you have where T : ISomeInterface, then this is constrained, and uses a special opcode. This means the interface can be used without boxing. For example: public static void Foo<T>(T obj) where T : ISomeInterface { … Read more
However, variant c does not, probably because the new function takes only values of the same type which is not the case since Fooer != i32. No, it’s because there is no new function for Box<dyn Fooer>. In the documentation: impl<T> Box<T> pub fn new(x: T) -> Box<T> Most methods on Box<T> allow T: ?Sized, … Read more
Internal Java implementation and could not be configured, the range is from -128 to 127. You can check Javadocs or simply take a look at sources: public static Integer valueOf(int i) { final int offset = 128; if (i >= -128 && i <= 127) { // must cache return IntegerCache.cache[i + offset]; } return … Read more
No, it does not exist. Actually, it was explicitly not implemented so as not to clutter the Stream API with tons of classes for every primitive type. Quoting a mail from Brian Goetz in the OpenJDK mailing list: Short answer: no. It is not worth another 100K+ of JDK footprint each for these forms … Read more
The Short Answer The key point is this: == between two reference types is always reference comparison More often than not, e.g. with Integer and String, you’d want to use equals instead == between a reference type and a numeric primitive type is always numeric comparison The reference type will be subjected to unboxing conversion … Read more