If the return type must be the type of the class that implements the interface, then what you want is called an F-bounded type: public interface A<T extends A<T>>{ public T b(); } public class C implements A<C>{ public C b() { … } } public class D implements A<D>{ public D b() { … … Read more
This behavior is underspecified but intended, though it might appear confusing. We plan to elaborate on the role of return type in macro signatures, but at the moment I feel like the flexibility is a good thing to have. Also at times the behavior is inconsistent, e.g. when the macro is caught in the middle … Read more
They’re hugely different. If you use dynamic you’re opting into dynamic typing, and thus opting out of compile-time checking for the most part. And yes, it’s less performant than using static typing where you can use static typing. However, you can’t do much with the object type anyway – it has hardly any members. Where … Read more
The answer is: you don’t need to provide overloads for ALL the numeric types, just for Double and Decimal. All others (except maybe some very unusually large ones) will be automatically converted to these. Not a base class but in fact that was the red herring. The base class System.ValueType doesn’t help much as it … Read more
“What are the differences between Integer and Int?” Integer is just an alias for java.lang.Integer. Int is the Scala integer with the extra capabilities. Looking in Predef.scala you can see this the alias: /** @deprecated use <code>java.lang.Integer</code> instead */ @deprecated type Integer = java.lang.Integer However, there is an implicit conversion from Int to java.lang.Integer if … Read more
It is the most generally used for library purpose. The main principe behind Opaque type in c is to use data though its pointer in order to hide data handling implementation. Since the implementation is hidden, you can modify the library without recompiling any program which depend on it (if the interface is respected) eg: … Read more
There are no aliases in Java. You can extend the HashMap class with your class like this: public class TheNewType extends HashMap<String, String> { // default constructor public TheNewType() { super(); } // you need to implement the other constructors if you need } But keep in mind that this will be a class it … Read more
Since IPv4 addresses are 4 byte long, you could use an INT (UNSIGNED) that has exactly 4 bytes: `ipv4` INT UNSIGNED And INET_ATON and INET_NTOA to convert them: INSERT INTO `table` (`ipv4`) VALUES (INET_ATON(“127.0.0.1”)); SELECT INET_NTOA(`ipv4`) FROM `table`; For IPv6 addresses you could use a BINARY instead: `ipv6` BINARY(16) And use PHP’s inet_pton and inet_ntop … Read more
Addressing questions one to three: one of the main applications for HLists is abstracting over arity. Arity is typically statically known at any given use site of an abstraction, but varies from site to site. Take this, from shapeless’s examples, def flatten[T <: Product, L <: HList](t : T) (implicit hl : HListerAux[T, L], flatten … Read more
No, a nullable is a struct. What is happening is that the nullable struct has two values: The value of the data type (int for int?, DateTime for DateTime?, etc.). A boolean value which tells if the data type value has been set. (HasValue is the property.) When you set the value of the data … Read more