My understanding with proto3 is that for scalars, there is no way to distinguish whether the message sender set a field to the default value or didn't set the field at all because default values aren't sent over the wire. That is, the hasField call for that field will return false regardless if the default value was set or not. And hasField will only return true if the field was set to something other than the default value.
I've read some stuff about using object as wrappers to get around this situation, but am still trying to understand how it'd work e.g: https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/wrappers.proto
My question is: if all the fields of an object happen to be set to their default values, will that object still be sent over the wire? Or will hasFields for that object return False?
A zero byte serialization is perfectly valid in protobuf. If nothing needs to be serialized because all fields are the default: you'll get zero bytes.
Related
I am creating an Alloy model of the iCalendar data format.
An iCalendar file contains properties. There are a lot of codependencies among the properties. I want to see if anything breaks when a property is removed (i.e., when the property is constrained to zero occurrences).
I want to write an assert and have the Alloy Analyzer search for counterexamples, but I am struggling with how to write the assert. I want the assert to say something like this:
If property X is removed (i.e., property X is constrained to zero
occurrences), there are no instances that are invalid as a result of
removing X.
In pseudocode, I want this:
assert NoProblemFilteringX {
(no prop: X | prop in iCalendar.properties) => all instances are still valid
}
Would you provide some guidance on formulating the desired assert, please?
Suggestion:
Write your codependency checks in a predicate taking as parameter a
set of properties. The predicate holds iff the codependencies are satisfied amongst those properties given in parameter.
Rewrite your fact ensuring those codependencies so as to call this predicate with the set of all iCalendar properties as parameters.
Call this predicate in the assert while this time giving iCalendar.properties - X as parameter
I'm trying to set up a save function in my HaxeFlixel game.
Some background: The object in question is an instance of Player, which extends FlxSprite. Save data is stored in an instance of a custom class I made for it. That instance is stored in a StringMap (the keys are save names), which is saved by serializing it to a variable in a FlxSave.
Creating the save data and writing it works fine. However, reading the save data back in crashes the game with the message "Invalid field: pixels". pixels is a field from FlxSprite, but it's not the first such field in the serialized string, so it's probably not that.
If it's useful, the declaration of that field is y6:pixelsn - that is:
y begin a field, which is named...
6: a string of length 6...
pixels (the string)
n null
From this line of code you can see that pixels is actually not a variable* at runtime. So the unserializer would crash when it tries to assign value to pixels. But more investigation is need on why the serializer serialized the pixels fields at the first place, because it shouldn't really exist at runtime.
Note*: the accessors of pixels are (get, set), which makes pixels not a real property at runtime. Read more here.
As a general rule, I don't recommend serializing a FlxSprite (or other complex objects) directly. Rather, you should extract the desired information (e.g. x/y position or hp, etc) and serialize only those.
I have set up a class that conforms to NSCoding, and works as expected when I first create the object. It is essentially the same set up as this
The problem I am having is that the properties of the object when changed are not kept.
For example,
Foo is created and has a property called name.
Foo.name = #"bar"
I can encode / decode the object and it retains the name bar.
If I try and change
Foo.name = #"newName"
The encode method is not called again, so foo.name remains as #"bar"
(I have a log state within the encode method)
Also,
I am using a core data object, that has a transformable property which points to the foo object.
Thanks
To "save" the object, you have to call the encode method, e.g. to write it to disk or send it to an output stream.
However, since you are using Core Data to persist the object, you have to call
[managedObjectContext save:&error];
to persist the object after changing it.
That being said, I do not think it makes a lot of sense to have a transformable property that points to a custom class that keeps a string property. Instead, you should think of a more appropriate data structure so you only need transformable properties for non standard data types that cannot be persisted by using the standard data types already built into Core Data.
I am working with the classes in the System.Windows.Documents namespace, trying to write some generic code that will conditionally set the value of certain dependency properties, depending on whether these properties exist on a given class.
For example, the following method assigns an arbitrary value to the Padding property of the passed FrameworkContentElement:
void SetElementPadding(FrameworkContentElement element)
{
element.SetValue(Block.PaddingProperty, new Thickness(155d));
}
However, not all concrete implementations of FrameworkContentElement have a Padding property (Paragraph does but Span does not) so I would expect the property assignment to succeed for types that implement this property and to be silently ignored for types that do not.
But it seems that the above property assignment succeeds for instances of all derivatives of FrameworkContentElement, regardless of whether they implement the Padding property. I make this assumption because I have always been able to read back the assigned value.
I assume there is some flaw in the way I am assigning property values. What should I do to ensure that a given dependency property assignment is ignored by classes that do not implement that property?
Many thanks for your advice.
Tim
All classes that derive from Block have the Padding property. You may use the following modification:
void SetElementPadding(FrameworkContentElement element)
{
var block = element as Block;
if (block == null) return;
block.Padding = new Thickness(155d);
}
Even without this modification everything would still work for you because all you want is for Padding to be ignored by classes that do not support it. This is exactly what would happen. The fact that you can read out the value of a Padding dependency property on an instance that does not support it is probably by design but you shouldn't care. Block and derivatives would honor the value and all others would ignore it.
Call to the function
setlocale(LC_MESSAGES , NULL)
returns ""(empty string) not Null or any locale.
why do i get this return value ?
is it because this feature is not implemented in the platform ?
On input to setlocale, the empty string "" represents the environment's default locale, which may differ from the minimal C locale represented by "C". It may be that setlocale has been called with the empty string and this is the platform's way of indicating that. However, one would hope or even expect that the string returned would be more informative, for example "en_US.UTF8".
Perhaps the information in the environment is ill-formed or not supported and this is the best that the system can do. The return value from the purported call to setlocale with the empty string as input should have been checked, as a failure at that point would have returned a null pointer.