How is setted the property descriptor for the built-in method? For example for isPrototypeOf? I did not find such a place in the specification. Rather found, but there is no description of the attribute [[Value]]. It sounds like this:
"Every other data property is described in clauses 18 through 26 and
in Annex B.2 has the attributes {[[Writable]]: true, [[Enumerable] ]:
false, [[Configurable]]: true} unless otherwise specified"
Now we know what the other attributes will have, but we do not know what value will be set in [[Value]]. You can say that the value in [[Value]] will be set to the function object and you will be right. However, I want to know by specification where this is the place where for built-in properties is set [[Value]]
However, I want to know by specification where this is the place where for built-in properties is set [[Value]]
The specification doesn't have algorithmic steps for initializing the global objects, which makes sense since they are expected to exist before execution of any code actually begins.
Instead of simply states what structure should exist, so for instance in 19.2.3 Properties of the Function Prototype Object, it simply states
19.2.3.1 Function.prototype.apply ( thisArg, argArray )
in the header with the expectation that it is clear that it means the apply function is a property of the %FunctionPrototype% global object. Given that, there are only two types of properties,
Accessor properties
Data properties
Data properties are explicitly simple properties that contain a value. Function.prototype.apply doesn't have get or set prefix, or use an ## prefix), which means that this statement is specifying a data string-keyed data property. By definition, this means that it is clear that the [[Value]] is the function object itself, because there is nowhere else to put it, and [[Value]] is the clear correct choice.
The section you linked in 17 ECMAScript Standard Built-in Objects states
Every other data property described in clauses 18 through 26 and in Annex B.2 has the attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true } unless otherwise specified.
is just filling in the rest of the data property fields, since it wouldn't make sense to repeat them for every single method.
Related
Example: What is the difference between :
List<UserCompany> findByCompany_IdAndCompany_IsActivated(params)
and
List<UserCompany> findByCompanyIdAndCompanyIsActivated(params)
There is no difference if your model is unambiguous with respect to field names.
List<UserCompany> findByCompanyIdAndCompanyIsActivated(params) -
this first thinks that companyId and companyIsActivated are properties within UserCompany and tries to find them if fails
it then thinks that UserCompany has a field Company - which is another class and Company has field - Id and IsActivated and tries to find them
Where as the below thing
List<UserCompany> findByCompany_IdAndCompany_IsActivated(params)
assumes directly that UserCompany has a field Company - which is another class and Company has field - Id and IsActivated and tries to find them
From the spring documentation
Property expressions :---
Property expressions can refer only to a direct
property of the managed entity, as shown in the preceding example. At
query creation time you already make sure that the parsed property is
a property of the managed domain class. However, you can also define
constraints by traversing nested properties. Assume Persons have
Addresses with ZipCodes. In that case a method name of
List findByAddressZipCode(ZipCode zipCode); creates the
property traversal x.address.zipCode. The resolution algorithm starts
with interpreting the entire part (AddressZipCode) as the property and
checks the domain class for a property with that name (uncapitalized).
If the algorithm succeeds it uses that property. If not, the algorithm
splits up the source at the camel case parts from the right side into
a head and a tail and tries to find the corresponding property, in our
example, AddressZip and Code. If the algorithm finds a property with
that head it takes the tail and continue building the tree down from
there, splitting the tail up in the way just described. If the first
split does not match, the algorithm move the split point to the left
(Address, ZipCode) and continues.
Although this should work for most cases, it is possible for the
algorithm to select the wrong property. Suppose the Person class has
an addressZip property as well. The algorithm would match in the first
split round already and essentially choose the wrong property and
finally fail (as the type of addressZip probably has no code
property). To resolve this ambiguity you can use _ inside your method
name to manually define traversal points. So our method name would end
up like so:
List findByAddress_ZipCode(ZipCode zipCode);
Underscore is reserved character which allows you to point the right object to construct jpa query. It's used only with nested objects. For example if you would like to query by ZipCode inside Address inside you Company object.
More information can be found here
Suppose I am binding using
bs.Bind(y)
.For(v => v.Visibility)
.To("Failures['TaxPercent'].Length")
.WithConversion("Visibility")
.WithFallback(false);
Where Failures is a dictionary which would contain the property name (e.g. TaxPercent) if, and only if, the property fails validation.
Therefore Failure['TaxPercent'] returns the validation failure message (e.g value missing).
I want to have an expandable textview in Android which is visible only when the error is detected. I used the above code and it is not working. The fallback value does not trigger when Failure['TaxPercent'] does not exist in the dictionary.
How do I get an expandable/collapsible textview based on the validation result using a dictionary in the viewmodel??? I would really like to use a dictionary because that would save me from creating IsErrorVisible for each property.
Oddly enough, using a dictionary works for retrieving the error message though, but not for visibility! In other words, this is working great
bs.Bind(y)
.For(v => v.Text)
.To("Failures['TaxPercent']");
Also, any reason why I cannot concatenate the binding, meaning can I do this???
bs.Bind(y)
.For(v => v.Text)
.To("Failures['TaxPercent']")
.For(v => v.Visibility)
.To("Failures['TaxPercent'].Length")
.WithConversion("Visibility")
.WithFallback(false);
EDIT
The error msg in the log is
MvxBind:Error:168.86 Problem seen during binding execution for binding Visibility for Failures['TaxPercent'].Length - problem ArgumentException: The value passed in must be an enum base or an underlying type for an enum, such as an Int32.
If the dictionary doesn't contain an entry for 'TaxPercent' then the expression Failures['TaxPercent'].Length will not evaluate (an exception will be throw) so UnsetValue will be used.
In the case of UnsetValue, the ValueConverter will not be called, and the Fallback will be used. This is the same pattern as in Wpf - http://msdn.microsoft.com/en-us/library/system.windows.dependencyproperty.unsetvalue(v=vs.110).aspx
For your particular situation, it looks like you could either:
change the Fallback to the correct value for the platform instead of to a boolean value (the question didn't specify which platform(s) you are using)
create a new Visibility ValueConverter that takes Failures as its binding source and 'TaxPercent' as its parameter
remove the .Length from your binding expression - just test on the existence of the entry.
you could switch to free text binding expressions - then you could do more complicated binding statements, including nested bindings, multiple value converters, multiple fallback values, ...
For this particular case, I would just drop the .Length
For "any reason why I cannot concatenate", that won't work as the return type of Bind is a single Fluent binding entry - not a Fluent binding set.
I seek to override a default setting in Octave concerning plots. For instance, I always set box off; when plotting, so I would like to set the box off by default. Perhaps factoryaxesbox is the involved setting (are those factory settings documented anywhere?).
When I see a setting returned by get(0, "factory"), how can I assign a new default to override this?
I have been through this section of the Octave manual, section 15.3.5: Managing Default Properties, but it says little and I find it rather confusing. Object type, root object, child object, … Huh?
Figured it out after some amount of trial and error.
The name of available properties for plots are those returned by get(0, "factory"), without the factory prefix. In order to override any of these, you must prefix the property name with default, in the format set(0, "defaultNameOfProperty", "newsetting").
To set box off by default for all plots:
set(0, "defaultaxesbox", "off")
Before doing this, if you check for the existence of this property defaultaxesbox, using get(0, "default"), you will find nothing, making you wonder if you can set a setting which does not seem to exist. After the assignment has been made with set(), it will show up in get(0, "default").
If the first argument of set() was gca() or some other number, then replace zero with that in the above get().
I have an interface named PropertyFilter which used to take a Propertyand decide if accepts it or not. And the world was good.
But now the interface changed, so that implementations may choose to add additional Propertys. For example a Customer property might get expanded into Name and Address properties.
I think it is obvious this is not a Filter anymore, but how would you call such a thing?
To clarify: the so called filter is pretty much a method with the signature
Property -> List<Property>
With an empty List denoting not accepting the Property, a List with exactly the input Property denoting accepting the property and a List with new Properties (possibly including the original one) denoting an expansion.
PropertyChecker
PropertyValidator
PropertyDistillator
PropertyAccreditor
...
Do you already have a name for the method you mention ? It might help us find a proper name for the interface as well.
I'm not really sure what your new function does. If it still returns a boolean, then another name for a function which returns a boolean value is a "predicate".
If it takes a Customer and decomposes it (perhaps you have one function which takes a Customer and returns a Name, and another which returns an Address), then I might call them "accessors". This term is often used to describe a member function of an object, but I think it could apply here, too.
If Customer has a Name and and Address, the it is no longer a property, but an entity.
The Customer property could be a reference to a Customer entity, in which case the semantic convention for your interface still apply.
I would add a method named validate to Property with the signature:
PropertyFilter -> Bool
The default implementation of validate simply passes this (the Property) to the filter and returns the result:
def validate (filter: PropertyFilter) = filter (this)
As a compound property, Customer overrides validate, implementing it in terms of its composite properties:
override def validate (filter: PropertyFilter) = name.validate (filter) && address.validate (filter)
This way, each Property can describe how to apply any given PropertyFilter to itself. I think you should avoid the List expansion approach.
While perusing an application that I'm documenting, I've run across some examples of bang notation in accessing object properties/methods, etc. and in other places they use dot notation for what seems like the same purpose.
Is there a difference or preference to using one or the other? Some simple googling only reveals limited information on the subject with some people actually using it in opposite cases. Perhaps there is a coding standards section from MS somewhere that indicates the method of madness?
Despite the (formerly) accepted answer to this question, the bang is not in fact a member or collection access operator. It does one simple and specific thing: The bang operator provides late-bound access to the default member of an object, by passing the literal name following the bang operator as a string argument to that default member.
That's it. The object doesn't have to be a collection. It doesn't have to have a method or property called Item. All it needs is a Property Get or Function which can accept a string as the first argument.
For much more detail and proof, see my blog post discussing this: The Bang! (Exclamation Operator) in VBA
The bang operator (!) is shorthand for accessing members of a Collection or other enumerable object, such as the Fields property of an ADODB.Recordset.
For example, you can create a Collection and add a few keyed items to it:
Dim coll As Collection
Set coll = New Collection
coll.Add "First Item", "Item1"
coll.Add "Second Item", "Item2"
coll.Add "Third Item", "Item3"
You can access an item in this collection by its key in three ways:
coll.Item("Item2")
This is the most explicit form.
coll("Item2")
This works because Item is the default method of the Collection class, so you can omit it.
coll!Item2
This is short-hand for both of the above forms. At run-time, VB6 takes the text after the bang and passes it as a parameter to the Item method.
People seem to make this more complicated than it should be, which is why it's hard to find a straightforward explanation. Usually the complications or "reasons not to use the bang operator" stem from a misunderstanding of how simple it actually is. When someone has a problem with the bang operator, they tend to blame it instead of the real cause of the problem they are having, which is often more subtle.
For example, some people recommend not using the bang operator to access controls on a form. Thus, Me.txtPhone is preferred over Me!txtPhone. The "reason" this is seen as bad is that Me.txtPhone will be checked at compile-time for correctness, but Me!txtPhone won't.
In the first case, if you mistype the code as Me.txtFone and there is no control with that name, your code won't compile. In the second case, if you wrote Me!txtFone, you won't get a compile error. Instead, your code will blow up with a run-time error if it reaches the line of code that used Me!txtFone.
The problem with the argument against the bang operator is that this problem has nothing to do with the bang operator itself. It's behaving exactly the way it's supposed to.
When you add a control to a form, VB automatically adds a property to your form with the same name as the control you added. This property is part of the form's class, so the compiler can check for typos at compile-time if you access controls using the dot (".") operator (and you can access them using the dot operator precisely because VB created a named control property for you).
Since Me!ControlName is actually short-hand for Me.Controls("ControlName")1, it should not be suprising that you don't get any compile-time checks against mistyping the control name.
Put another way, if the bang operator is "bad" and the dot operator is "good", then you might think
Me.Controls("ControlName")
is better than
Me!ControlName
because the first version uses a dot, but in this case, the dot isn't any better at all, since you are still accessing the control name via a parameter. It's only "better" when there is an alternative way to write the code such that you will get compile-time checking. This happens to be the case with controls due to VB creating properties for each control for you, and this is why Me.ControlName is sometimes recommended over Me!ControlName.
I had originally stated that the Controls property was the default property of the Form class, but David pointed out in the comments that Controls isn't the default property of Form. The actual default property returns a collection that includes the contents of Me.Controls, which is why the bang short-hand still works.
Couple gotchas to serve as addenda to the two exceptional answers already posted:
Accessing recordset fields in forms vs. reports
The default item of Form objects in Access is a union of the form's Controls collection and the form recordset's Fields collection. If the name of a control conflicts with the name of a field, I'm not sure which object is actually returned. Since the default property of both a field and a control is their .Value, it's often a "distinction without a difference." In other words, one normally doesn't care which it is because the values of the field and control are often the same.
Beware of naming conflicts!
This situation is exacerbated by Access's Form and Report designer defaulting to naming bound controls the same as the recordset field to which they are bound. I've personally adopted the convention of renaming controls with their control type prefix (e.g., tbLastName for the text box bound to the LastName field).
Report recordset fields aren't there!
I said earlier the Form object's default item is a collection of Controls and Fields. However, the Report object's default item is only its collection of Controls. So if one wants to refer to a recordset field using the bang operator, one needs to include that field as the source for a (hidden, if desired) bound control.
Beware conflicts with explicit form/report properties
When one adds controls to a form or report, Access automatically creates properties that refer to these controls. For example, a control named tbLastName would be available from a form's code module by referring to Me.tbLastName. However, Access will not create such a property if it conflicts with an existing form or report property. For example, assume one adds a control named Pages. Referring to Me.Pages in the form's code module will return the form's Pages property, not the control named "Pages".
In this example, one could access the "Pages" control explicitly using Me.Controls("Pages") or implicitly using the bang operator, Me!Pages. Be aware, though, that using the bang operator means that Access might instead return a field named "Pages" if one exists in the form's recordset.
What about .Value?
Though not explicitly mentioned in the question, this topic came up in the above comments. The default property for Field objects and most "data-bindable"¹ Control objects is .Value. Since this is the default property, VBA will implicitly return the .Value property's value when it does not make sense to return the object itself. Thus, it's common practice to do this...
Dim EmployeeLastName As String
EmployeeLastName = Me.tbLastName
...instead of this...
EmployeeLastName = Me.tbLastName.Value
The above two statements produce identical results because EmployeeLastName is a string.
Beware the subtle .Value bug when keying dictionaries
There are some cases where this convention can cause subtle bugs. The most notable--and, if memory serves, only--one I've actually run into in practice is when using the value of a Field/Control as a Dictionary key.
Set EmployeePhoneNums = CreateObject("Scripting.Dictionary")
Me.tbLastName.Value = "Jones"
EmployeePhoneNums.Add Key:=Me.tbLastName, Item:="555-1234"
Me.tbLastName.Value = "Smith"
EmployeePhoneNums.Add Key:=Me.tbLastName, Item:="555-6789"
One would likely expect that the above code creates two entries in the EmployeePhoneNums dictionary. Instead, it throws an error on the last line because we are trying to add a duplicate key. That is, the tbLastName Control object itself is the key, not the value of the control. In this context, the control's value does not even matter.
In fact, I expect that the object's memory address (ObjPtr(Me.tbLastName)) is likely what's being used behind the scenes to index the dictionary. I did a quick test that seems to bear this out.
'Standard module:
Public testDict As New Scripting.Dictionary
Sub QuickTest()
Dim key As Variant
For Each key In testDict.Keys
Debug.Print ObjPtr(key), testDict.Item(key)
Next key
End Sub
'Form module:
Private Sub Form_Current()
testDict(Me.tbLastName) = Me.tbLastName.Value
Debug.Print ObjPtr(Me.tbLastName); "..."; Me.tbLastName
End Sub
When running the above code, exactly one dictionary item is added each time the form is closed and re-opened. Moving from record to record (and thus causing multiple calls to the Form_Current routine) does not add new dictionary items, because it is the Control object itself indexing the dictionary, and not the Control's value.
My personal recommendations/coding conventions
Over the years, I've adopted the following practices, YMMV:
Prefix Form/Report control names with control type indicators (e.g., tbTextBox, lblLabel, etc.)
Refer to Form/Report controls in code using Me. notation (e.g., Me.tbLastName)
Avoid creating table/query fields with problematic names in the first place
Use Me! notation when there are conflicts, such as with legacy applications (e.g., Me!Pages)
Include hidden report controls to gain access to report Recordset field values
Explicitly include .Value only when the situation warrants the added verbosity (e.g., Dictionary keys)
¹ What's a "data-bindable" control?
Basically, a control with a ControlSource property, such as a TextBox or ComboBox. A non-bindable control would be something like a Label or CommandButton. The default property of both a TextBox and ComboBox is .Value; Labels and CommandButtons have no default property.