AS3 provide several way to handle something like java Map, but what's the difference with Dictionary, Object and dynamic?
An Object can be used as a map, where the key is a simple string. An objects purpose though is not solely to work as a map, it just happens, that you can use it as such.
A Dictionary is a key/value map, where the key can be an object, too. This is useful, if you want to find values based on a specific object, that you have. The purpose of a Dictionary really is, to be used as a map.
The 'dynamic' keyword is used to make your own class be extendable in the way, that you can put things into an instance of that class at run-time. Something, which you cannot do, if you do not use the keyword 'dynamic'.
Related
Suppose I have a simple map, example-map:
(def example-map {"s" {"f" "g"}
"m" {"r" "q"}})
I can use clojure.data.json/write-str to JSON-ify this map as such:
(clojure.data.json/write-str example-map) =>
"{\"s\":{\"f\":\"g\"},\"m\":{\"r\":\"q\"}}"
I'd like to conditionally place some of the values into lists according to the value of their keys.
write-str provides an optional :key-fn, which applies some function to key value pairs. For example, the desired function might specify that all values associated with entries that match "s" are placed in lists.
(clojure.data.json/write-str example-map :key-function desired-function) =>
"{\"s\":[{\"f\":\"g\"}],\"m\":{\"r\":\"q\"}}"
Does anyone know how to specify such a key function that checks for membership of a key in a set and places the values associated with members into an array rendered in the output JSON?
Like your previous question, this is not a job for the JSON parser. You don't need to rely on write-time features of your JSON library to adjust the shape of your JSON maps. Instead, you have a fully functional Turing complete language at your disposal: Clojure! If the maps don't already look the way you want them to be output, then write a function that takes one Clojure map as input and produces a different one as output; then ask your JSON library to write the output map, without any special rules for fiddling with the output.
Now, as it happens this particular JSON library does provide an option named value-fn (not key-function as you claim) to let you modify a value in a map based on its key. So you could use that, in which case you simply need to write a function with a signature like:
(fn [k v]
(...compute new value...))
There are many ways you could write such a function, but they are all entirely divorced from your JSON parser. If you need help writing it, mention some specific things you need help with, so you can get a clear explanation for the part of the process that is actually giving you trouble.
I got an anonymous array which I want to deserialize, here the example of the first array object
[
{ "time":"08:55:54",
"date":"2016-05-27",
"timestamp":1464332154807,
"level":3,
"message":"registerResourcePath ('', '/sap/bc/ui5_ui5/ui2/ushell/resources/')",
"details":"","component":"sap.ui.ModuleSystem"},
{"time":"08:55:54","date":"2016-05-27","timestamp":1464332154808,"level":3,"message":"URL prefixes set to:","details":"","component":"sap.ui.ModuleSystem"},
{"time":"08:55:54","date":"2016-05-27","timestamp":1464332154808,"level":3,"message":" (default) : /sap/bc/ui5_ui5/ui2/ushell/resources/","details":"","component":"sap.ui.ModuleSystem"}
]
I tried deserializing using CL_TREX_JSON_SERIALIZER, but it is corrupt and does not work with my JSON, here is why
Then I tried /UI2/CL_JSON, but it needs a "structure" that perfectly fits the object given by the JSON Object. "Structure" means in my case an internal table of objects with the attributes time, date, timestamp, level, messageanddetails. And there was the problem: it does not properly handle references and uses class description to describe the field assigned to the field-symbol. Since I can not have a list of objects but only a list of references to objects that solution also doesn't works.
As a third attempt I tried with the CALL TRANSFORMATION as described by Horst Keller, but with this method I was not able to read in an anonymous array, and here is why
My major points:
I do not want to change the JSON, since that is what I get from sap.ui.log
I prefere to use built-in functionality and not a thirdparty framework
Your problem comes out not from the anonymity of array, but from the awkwardness of SAP JSON (De)serializer, which doesn't respect double quotes, which enclose JSON attributes. The issue is thoroughly described in this answer.
If you don't want to change your JSON on-the-fly, the only way you have is to change CL_TREX_JSON_DESERIALIZER class like this.
/UI5/CL_JSON_PARSER parses JSONs with unknown format.
Note that it's got "for internal use" written on it so many times that you probably should take it seriously and clone its code to fixate it.
Let's say I have a JSONObject in GWT that looks like this: {"name1":value1, "name2":value2}. Is there a way to remove the "name2":value2 key/value pair and change this object to {"name1":value1}? I have not found any methods that help with this approach in the GWT Javadoc.
I know there are workarounds to this, of course. Since my JSONObject is small, I am currently making a new one and putting in it all the key/value pairs other than the one I want to remove. But this won't work when I plan to pass in the JSONObject to a child function; since only the JSONObject's reference is passed in Java, I need a mutator function to actively change what the method parameter's JSONObject points to. In the worse case, I could convert the JSONObject to a String and regexp out what I don't want. But this seems prone to error and ugly. Any suggestions?
Actually, put()ing a null (as opposed to a JSONNull) value will delete the value for the given key.
I'm writing an application where I have many objects (data models) that are identified by a unique String ID that every such object possesses and these objects can refer to each other by their IDs.
So far so good but now I need to keep track of which object keeps a reference to another object and of course there are cases where an object references (or is referenced by) more than one other object and I was wondering what would be the best method to store these references? In a simple map data structure I could just map one object's ID to another but as mentioned there are cases where an object can hold a ref to an arbitrary amount of other objects. Or I could map another map or an Array that hold more than one reference but I'd like to prevent iteration and maybe somebody knows a much better solution for this.
I guess it depends a lot in the particular use, but I think a Dictionary is the way to go, unless you need the order of the references, in which case I think an Array (or Vector) should work...
//Array:
object1.references.push(object2);
for each(var o in object1.references) trace(o);
object1.references.pop();
//Dictionary:
object1.references[object2] = 1;
for (var o in object1.references) trace(o);
delete object1.references[object2];
Whenever you have a dynamic arbitrary set of objects, I think you will necessarily need to iterate through them, whether its an array, object or dictionary.
When I'm working with Hash Tables/Dictionaries I sometimes struggle with how to specify keys.
For example: if I create a simple Dictionary (using Python for this example),
foo = {'bar': 'baz', 'foobar': 'foobaz' }
I can access values (in other modules) with the key values: (foo['bar']) and get baz back.
In the words of Dr. Evil, "pretty standard, really."
Unfortunately, using static strings for keys tightly couples any modules using this Dictionary to its implementation. Of course, this can also apply when using other key types (e.g. Enums, Objects, etc.); anyway you slice it, all modules which access the Dictionary need to know the values for the keys.
To resolve this, I typically use static constant string values (or Enums if available in the language) for keys, and either store them publicly in the local class/module, or in a separate module/class. Therefore any changes to the dictionary keys themselves are kept in a single location.
This usually looks like this:
BAR_KEY = 'bar'
foo[BAR_KEY] = 'foobar'
Are there better ways of specifying keys such that the use of the Dictionary doesn't necessarily couple a module/class to its implementation?
Note: I've seen a few responses in SO which address this (e.g. property-to-reference-a-key-value-pair-in-a-dictionary), but the topics didn't seem to address this issue specifically. The answers were helpful, but I'd like a wider range of experience.
Why not make a class for this, which only contains properties? This is done nicely with Python (from what I know), and works well with other languages, too. Refactoring the names is trivial with today's tools, too.
In cases where I'm passing the object around and I've got known keys, I'd always prefer adding an attribute to an object. IMO, the use case of dictionaries is when you don't know what the keys are.
Python is trivial:
foo.bar=baz
Java is pretty much the same:
class Foo { public String bar="baz"; }
The Python performance would be pretty much identical, since a property lookup is just a dictionary lookup and the Java performance would be better.
I sometimes create a separate class to hold the dictionary keys. That gives them their own namespace, as well as the regular benefits of having the keys be in const strings, namely that you don't have the risk of typos, you get code completion, and the string value is easy to change. If you don't want to create a separate class, you get all of the benefits except a namespace just from have const strings.
That said, I think you're getting close to soft coding territory. If the keys in the dictionary change, it's OK for code using the dictionary to change.
Personally, I use your method. It's pretty sensible, simple, and solves the actual problem.
I usually do the same thing; if the key is always going to be the same, make a 'constant static' in whatever language to hold the key.