From Ada2012 Reference Manual:
arm2012.html/rm-4-1-3.html
A selected_component that is not an expanded name shall resolve to denote one of the following:
A view of a subprogram whose first formal parameter is of a tagged type or is an access parameter whose designated type is tagged:
Why it is significant to have it only for the first formal parameter?
Please explain with examples.
The definition in 4.1.3 Selected Components, 9.1/2 provides for prefixed notation, which allows one to invoke the primitive operations of a tagged type without mentioning the enclosing package explicitly. A related example is seen here.
Related
I know about https://www.javadoc.io/doc/io.vavr/vavr/latest/io/vavr/Value.html#toJavaArray but it's deprecated. Is there a non-deprecated method that can be used?
Out of the three toJavaArray variants, only the toJavaArray(Class) variant is deprecated directly, the other two are marked as deprecated because the Value class itself is deprecated. The generated javadoc is not very helpful in distinguishing between the two, unfortunately, but you can check the source code directly. This picture is probably a more precise representation of the current state:
Value is deprecated in favor of io.vavr.Iterable. This new interface is an extension of the java.lang.Iterable type, that differs mainly in that it returns an io.vavr.collection.Iterator instead of a simple java.util.Iterator. io.vavr.collection.Iterator extends Value, and I expect that after the removal of the Value interface, all methods which are not explicitly deprecated in the Value interface will be moved to io.vavr.collection.Iterator.
Out of the two not explicitly deprecated toJavaArray methods I would use the T[] toJavaArray(IntFunction<T[]> arrayFactory) variant – which was one of my contributions to the vavr project –, as it returns a typed array of the correct type instead of an Object[].
To sum it up, instead of using vavrValue.toJavaArray(), I would use vavrValue.iterator().toJavaArray(SomeType[]::new).
I have a schema that has many complexType, some of which have subtypes (via xsi:type). I need to create an XQuery expression that checks that an element (MyPath) is a member of a parent type, but no others, I've tried an expression in the form below with no luck.
/MyPath[element(*,ParentClass) and not element(*,ChildClass)]
It appears element applies to all the children in the context it is called, but not itself (MyPath), which yields no results.
I also tried the instance of operator, but this appears to only work for simpleType.
You should use
. instance of element(*, ParentClass)
and not(. instance of element(*, ChildClass))
If this doesn't work please supply an MCVE
An alternative, using Saxon extension functions, is to test the type annotation directly: saxon:type-annotation(.) eq xs:QName('ParentClass')
Of course, there's a question about whether this is good practice. The whole point of defining a derived type is that it is supposed to be substitutable for the base type; everywhere you can use an instance of the parent type, you should be able to substitute an instance of the child type. You appear to be deliberately trying to contrive a query in which this is not the case.
In this question about the passing of arguments in JavaScript functions, we learn that everything is passed by value in JavaScript.
In Mozilla documents, it is mentioned that the primitive types are immutable, and objects are. Although I came from the procedural and structured programming school, I was able to quickly pick up the concepts.
In the ECMAScript standard, it is defined that "An Object is 'logically' a collection of properties". The standard also defines how objects may be compared, but left out on what happens when an object goes through the GetValue() pseudo-function that converts references into values.
So, I gave an answer in the question basically saying that this area had been left undefined.
My Question
I feel that by "left undefined", I meant, it wasn't philosophically thoroughly clear, what the value of an Object is. The standard had gone through a few revisions, and its size is ever increasing.
In short, an object is a collection, but what is the value of the collection? Is it the makeup of its content? Or is it individuality? Or have I been missing out on some important texts?
In the ECMAScript spec, every object is defined to have certain 'internal methods', some of which (e.g., [[DefineOwnProperty]] and [[Put]]) can change the state of the object. Ultimately, the mutability of objects is defined via the use of such internal methods.
GetValue() doesn't leave out what happens to objects -- step #1 is:
If Type(V) is not Reference, return V.
So it you pass it an object, you get back the same object.
(Which refutes one of your premises, but I'm not sure it resolves your question.)
See section 4.3.26 "property" of the 5.1 edition. The note says:
Depending upon the form of the property the value may be represented either directly as a data value (a primitive value, an object, or a function object) or indirectly by a pair of accessor functions.
We can take this as meaning a data value is one of the following:
Primitive Value: such as C language double, _Bool, ((void*)0), etc.
An object: which can be interpreted as a special C language structure containing the underlaying information about the object.
Function object: which is just a special case of 2, possibly the result of JIT compilation.
The reason this note for the definition of property is important, is because, everything - even function block scopes - are objects (or at least described in terms of one). Therefore, if we can determine that "the value of an object" is its individuality rather than its content makeup, then with the fact that every object accessible from a JavaScript program, is accessed as if its the property of some other object.
In section 4.2 "Language Overview", it says:
A primitive value is a member of one of the following built-in types: Undefined, Null, Boolean, Number, and String; an object is a member of the remaining built-in type Object; and a function is a callable object.
Although this is an informal section, it can be seen that an object differs from a primitive value in a significant way.
As an interpretation, let's consider the value of an object is the object itself as we can infer from the "GetValue()" pseudo function - the overview says "an object is a member of the ... type Object - therefore, the value is the membership to the Object type.
To use a physics analogy to explain the relationship between membership and individuality, we see too electrons. They are identical in content, they're both the members of the Universe, yet they are two different individuals.
Therefore, we infer that - the value of a JavaScript Object, is its individuality.
Finally as to the question as asked in the title.
The mutibility of individual objects is defined in terms of a series of specificational pseudo functions, and immutability of other types is defined using the definition of value membership of types and specification pseudo functions operating on the primitive type values.
I was reading about Java 8 features, which lead me to this article and I was wondering about the actual uses of constructor reference, I mean why not just use new Obj ?
P.S, I tried googling, but I failed to find something meaningful, if someone has a code example, link or tut it will be great
First of all, you should understand that constructor references are just a special form of method references. The point about method references is that they do not invoke the referenced method but provide a way to define a function which will invoke the method when being evaluated.
The linked article’s examples might not look that useful but that’s the general problem of short self-contained example code. It’s just the same as with the “hello world” program. It’s not more useful than typing the text “hello world” directly into the console but it’s not meant to be anyway. It’s purpose is to demonstrate the programming language.
As assylias has shown, there are use cases involving already existing functional interfaces using the JFC API.
Regarding the usefulness of a custom functional interface that’ll be used together with a constructor reference, you have to think about the reason to use (functional) interface in general: abstraction.
Since the purpose of an interface is to abstract the underlying operation, the use cases are the places where you do not want to perform an unconditional new SomeType(…) operation.
So one example is the commonly known Factory pattern where you define an interface to construct an object and implementing the factory via constructor reference is only one option out of the infinite possibilities.
Another important point are all kinds of Generic methods where the possibility to construct instances of the type, that is not known due to type erasure, is needed. They can be implemented via a function which is passed as parameter and whether one of the existing functional interfaces fits or a custom one is needed simply depends on the required number and types of parameters.
It's useful when you need to provide a constructor as a supplier or a function. Examples:
List<String> filtered = stringList.stream()
.filter(s -> !s.isEmpty())
.collect(Collectors.toCollection(ArrayList::new)); //() -> new ArrayList<> ()
Map<String, BigDecimal> numbersMap = new HashMap<>();
numbersMap.computeIfAbsent("2", BigDecimal::new); // s -> new BigDecimal(s)
someStream.toArray(Object[]::new); // i -> new Object[i]
etc.
I have to work with Dynamics 2012 r3 and x++ and I wonder:
what is "::" - its inherit, implementation or what?
why some variables are write like "_vensGroup" - that _ means something or this is just convention?
:: is a scope. It allows you to use class method (on tables and classes). The point is used to call an object method.
The scope is also used to call values on BaseEnum.
_ is a prefix for parameters. It's a convention. It allows you to recognize local variable and parameters. As parameters are not ment to be changed in a method (they are passed by value), you will always be able to distinguish it from local variables and use them in your code.
To answer both questions:
:: is a scope dereference to a (static) method (as opposed to . which dereferences a variable, constant or property), usually for the Global scope, but it could be for other similar scopes. It is reserved.
The underscore prefix is just a naming convention. It is not part of the language.
Regarding your underscore question:
A widely spread convention is to use leading underscores to indicate passed parameters e.g.
public void foobar(int _myInt, str _myStr)
{
...
}
See here for the best practice MSDN page describing this convention.
In addition to the other answers to your question, :: is used not only to call to static table/class methods, but for other purposes as well, e.g. call methods in maps or reference enums.