I'm trying to understand get_instance_id()
and I came across this line in the documentation:
This ID can be saved in EncodedObjectAsID, and can be used to retrieve
the object instance with #GDScript.instance_from_id.
I can't seem to understand what this statement means exaclty and how to use EncodedObjectAsID, could someone please provide a working example?
The EncodedObjectAsID follows a pattern called Boxing. Boxing is where you put a primitive value, like an int, into an object. This boxed primitive can now be used in an object oriented way. For example, you can pass the boxed int to a function that only takes objects (i.e. it applies Polymorphism):
func only_takes_object(obj: Object)
only_takes_object(123) # Error
var box = EncodedObjectAsID.new()
box.object_id = 123
only_takes_object(box) # Valid
This is how parts of the editor use the EncodedObjectAsId object.
In marshalls.cpp we can see that an encoded Object may be an integer ID or the whole object. When it is flagged as only an integer ID a EncodedObjectAsID object is created. This object is then converted to a Variant.
When adding a stack variable in editor_debugger_inspector.cpp a variant with a type of object is assumed to be and converted to an EncodedObjectAsID to fetch the referenced object's id.
Here's two more links that follow a similar pattern:
array_property_edit.cpp
scene_debugger.cpp
Note that Variant can be implicitly converted to an Object and Object::cast_to() only takes Objects.
This ID can be saved in EncodedObjectAsID, and can be used to retrieve the object instance with #GDScript.instance_from_id.
This sentence should be split into two independent clauses. It should read as
"The instance ID can be saved in an EncodedObjectAsID."
"The instance ID can be used to retrieve the object instance with #GDScript.instance_from_id()."
Note: You should not store an object's id in storage memory. There is no guarantee that an object's id will remain the same after restart.
Related
Is there a way to determine the Object type, when passing a reference to a function?
I'm using a security permissions function, which determines if the user has permission to view/edit the Form passed to it by reference. I'd like to expand this to include reports as well.
To keep the function generic, I'd like to pass a ref for either a Form or a Report as an Object, eg:
function gfSecurity_Permission(obj as Object)
However, I'd need to determine the type of the object within the function.
Does anyone know of a way to do that?
MTIA
Take a look at
typeOf and typeName
Generic object variables (that is, variables you declare as Object)
can hold objects from any class. When using variables of type Object,
you may need to take different actions based on the class of the
object; for example, some objects might not support a particular
property or method. Visual Basic provides two means of determining
which type of object is stored in an object variable: the TypeName
function and the TypeOf...Is operator.
TypeName and TypeOf…Is
The
TypeName function returns a string and is the best choice when you
need to store or display the class name of an object, as shown in the
following code fragment:
Dim Ctrl As Control = New TextBox
MsgBox(TypeName(Ctrl))
The TypeOf...Is operator is the best choice for testing an object's
type, because it is much faster than an equivalent string comparison
using TypeName. The following code fragment uses TypeOf...Is within an
If...Then...Else statement:
If TypeOf Ctrl Is Button Then
MsgBox("The control is a button.")
End If
Simplest way to determine the access type in access is to do an object lookup within the Access' system tables.
Here would be the lookup:
DLookup("Type","MSysObjects","NAME = '" & strObject & "'")
strObject is the name of the object within Access
The result is one of the number below OR NULL if the object does not exist in Access
1 = Access Table
4 = OBDB-Linked Table / View
5 = Access Query
6 = Attached (Linked) File (such as Excel, another Access Table or query, text file, etc.)
-32768 = Access Form
-32764 = Access Report
-32761 = Access Module
so, the dlookup would provide "-32768" for a Form or "-32764" for a Report
Hope that helps
I have a hash map which acts as store of objects - where key is class name & value is object
store = {} of String => Type
store["Animal"]= Animal.new
store["Book"]= Book.new
store["Car"]= Car.new
Here class is unknown to me, which means i can't use union type. Please tell me how to solve this problem ?
I am trying to create a wrapper around hash map for storage of objects, which will save object & return object by key.
Update 1
Classes will be passed as a parameter - like this
add_in_store(Animal)
add_in_store(Person)
Update 2
Crystal play link of what i am trying to do - https://play.crystal-lang.org/#/r/8lwx
Solution of problem doesn't have to be in same way as what i m doing. It can be with any other approach like using proc or macro etc.
Hash is a generic type, to wrap it in a way where you cannot or don't want to restrict the possible types of the generic arguments, you should make your wrapper itself generic.
class Store(V)
#store = {} of String => V
def add(name, value : V)
#store[name] = value
end
end
Then the consumer of your wrapper has to give the possible types.
assert.deepStrictEqual(actual, expected[, message]) in nodejs's docs:
Type tags of objects should be the same.
what's the meaning of "type tags"
const date = new Date();
const object = {};
const fakeDate = {};
Object.setPrototypeOf(fakeDate, Date.prototype);
// Different type tags:
assert.deepStrictEqual(date, fakeDate);
typeof date and typeof fakeDate ,The results are all object, but different type tags
Type tags in Javascript, are referred to the word returned by typeof
For example for primitive values:
typeof({}) // returns 'object', this is the type tag
For non-primitive:
Object.getPrototypeOf(new Date) // returns 'Date {}' this is the type tag
If typeof is used with Date it will returns object which is right, because that would be the type tag for the primitive value, this is why using Object.getPrototypeOf is more accurate.
In the firsts JS implementations, the type tag were stored the first 1–3 bits and the the remaining 29–31, contained the actual data.
What the NodeJS docs says, it's that the result of Object.getPrototypeOf function when comparing two objects has to be the same to be considered as equal.
This is an old question that has been already answered, but I thought I might add that, although:
In the first implementation of JavaScript, JavaScript values were
represented as a type tag and a value. The type tag for objects was 0.
null was represented as the NULL pointer (0x00 in most platforms).
Consequently, null had 0 as type tag, hence the typeof return value
"object".
Type tags can also refer to an object's toStringTag.
The Symbol.toStringTag well-known symbol is a string valued property
that is used in the creation of the default string description of an
object. It is accessed internally by the Object.prototype.toString()
method.
The value associated to the well-know Symbol.toStringTag is used as the default string description of an object. Since every built-in object has a toStringTag value (except for null prototypes), it can be used to detect an object's class.
There's a package called typetags that has more information about it: typetags.org
I have started using NSIncrementalStore. When you process a fetch request, you first have to process the predicate to get your internal reference objects. Then you convert these to objectID's and then you ask the context to get the corresponding managedObjects. At least that is my interpretation of the available documentation.
let fetchedReferences : [Int] = Array(names.keys) //names represent my backingstore
var fetchedObjectIDs : [NSManagedObjectID] = []
for reference in fetchedReferences
{
fetchedObjectIDs.append(self.newObjectIDForEntity(request.entity, referenceObject: reference))
}
var fetchedObjects : [NSManagedObject] = []
for objectID in fetchedObjectIDs
{
fetchedObjects.append(context.objectWithID(objectID))
}
"newObjectIDForEntity" is also used to obtain permanent objectID's (see obtainPermanentIDsForObjects)
I want to know what "newObjectIDForEntity" does. Does it make a new instance for the same object or does it each time internally create a new object? What I mean is this: if I create a new managed object and then fetch the object, I will have called "newObjectIDForEntity" twice for the same object. Does core data now think there are 1 or 2 objects?
Does it make a new instance for the same object or does it each time internally create a new object?
newObjectIDForEntity:referenceObject: is one of two utility methods for mapping between the store's internal representation of a managed object snapshot and an NSManagedObjectID. It's inverse is referenceObjectForObjectID:. As you might guess from the name, newObjectIDForEntity:referenceObject: returns an object considered to have a retain count of 1. newObjectIDForEntity:referenceObject: calls an internal factory method for generating an NSManagedObjectID that is unique to that reference object in this persistent store. Once that has been done, referenceObjectForObjectID: can look up that NSManagedObjectID and return the reference object it represents.
What I mean is this: if I create a new managed object and then fetch the object, I will have called "newObjectIDForEntity" twice for the same object. Does core data now think there are 1 or 2 objects?
I assume you mean an NSManagedObjectContext that is using your store creates the managed object. You can call newObjectIDForEntity:referenceObject: as many times as you want, the NSManagedObjectID instance may be different, but the data it represents is unchanged. It will know that it points to the same reference object as an earlier call with the same reference data and entity description.
I've got a problem here. (C#)
There's a collection in another assembly (I cannot change it) that takes a string as parameter and returns an object.
Like:
object Value = ThatCollection.GetValue("ParameterName");
The problem is, for each parameter string, it returns a DIFFERENT type as object.
What I want is to cast those objects to their respective types, knowing the types only at runtime by their string names.
I need to do some operations with those returned values.
And for that I need to cast them properly in order to access their members and so.
Limitations:
I cannot use "dynamic" since my code needs to be done in an older framework: 3.5 (because of interop issues).
I need to do operations with MANY returned values of different types (no common interfaces nor base classes, except "object", of course)
All I have is a table (containing string values) correlating the parameter names with their returned types.
Yes, I could transform that table into a biiig "switch" statement, not very nice, don't want that.
Any hints??
You want to look into reflection, something like the following should work to cast an object to type T. Set up a simple cast method:
public static T CastToType<T>(object o)
{
return (T)o;
}
Invoke this using reflection:
Type t = Type.GetType(stringName)
MethodInfo castTypeMethod = this.GetType().GetMethod("CastToType").MakeGenericMethod(t);
object castedObject = castTypeMethod .Invoke(null, new object[] { obj });