I want to renew a variable if it is outdated - obviously this could be done with storing its creation time.
However - is there a (possilby undocumented) way of figuring out WHEN a variable in workspace was declared?
No, there is no way to know when a variable was created. People have explored the array metadata in detail, and nobody has found any indication of creation time stamps.
Furthermore, such a data field has no uses in general, and therefore are unlikely to be implemented, as a time stamp would just take up memory without providing a benefit.
For the very few cases where such a time stamp would be useful, I’d recommend creating a class that behaves like a normal numeric array, but additionally carries a time stamp.
Related
I am thinking about how to best represent a certain data structure efficiently in Swift using CoreData. What I need is work with accounts (like savings, earning etc.). So what would probably make sense is an account class, where each account instance might have multiple characteristics like e.g. ACCOUNT_TYPE_ID which do not change. The core however is the VALUE attribute, which would hold the value of the account at a certain point in time. The complex thing here is that this value obviously might change over time (lets say on a daily basis, abstracting for intra-day changes) and I would need to be able to get the value of each instance for any given date. E.g. I might have my savings_private for which I would want to get the value at each month-end. This value might have changed, but as well could stay the same for various days/months. How could this most efficiently (when it comes to used space but - and that is even more important - be able to access computationally efficient) be done with a CoreData Entity/Class? I was thinking about maybe always starting with zero and then only somehow save the changes plus the date of change and then have some method for the call which would add all changes up to a date parameter - but was curious about what a best-practice might be here, as I guess I am not the first one trying to solve this.
I am writing an app that requires access to a set of information from all classes and methods.
My query is, what's the most efficient way of doing this, so as to minimise memory usage?
I have taught myself coding and have, of course, come across numerous different methods to solve this whilst trawling the internet. For example:
I could create a global variable such as var info = ..., which I'd place above a class definition, thus giving access from anywhere in the app.
Or I could create a singleton, GameData and have the data stored there, e.g. GameData.shared.info, similarly available from anywhere in the app.
Or I could load the information in the first ViewController and then pass it around as a parameter.
There are no doubt more methods that I haven't come across, but I wonder which is the most memory-efficient method, if indeed there is such a thing. In my case, I won't need access to a huge amount of data - no more than say sixty or seventy records each with half a dozen fields of text or numbers.
Many thanks
Using dependency injection, that is, passing it as a parameter to any object that requires it, would be the more memory conscious method, since the variable will stop existing "automatically" if you were to replace the whole hierarchy (as long as it's done correctly).
By using a singleton or a global variable, you would have to clear the value yourself.
If the value is not going to disappear during the lifetime of the application, then memory usage doesn't matter, but I would still advice against global variables and suggest using dependency injection.
The usecase
We got multiple changelogs stored in the database, and want to create a histogram monitoring the duration between changes.
The problem
There doesn't seem to be a way to set the start time of a Historgram.Timer, e.g we want to set it to lastUpdated given the current changelog.
Avenues of approach
1 Subclassing Histogram
Should work. However the java-lib use protected/package-private extensively, thus making it hard without copying large portions of the library.
2 Using reflection
After a Histogram.Timer is created it should be possible to use reflection to set the start field. The field is marked as private final, and thus a SecurityManager could stop us in some environments.
Ideas?
Neither of the solutions seems like the correct way to go, and I suspect that I'm overlooking a simpler solution (but could find anything at SO or google). We're using grafana to visualize our metrics, if thats at all helpful in this scenario.
You don't need to subclass Histogram, as you don't need to use Histogram.Timer only because your histogram is measuring times.
Simply call myHistogram.observe(System.now() - lastUpdated) every time you record a new change in the database.
In official documentation I can't find any information how to write conditional statements for java.util.Date type fact fields in guided rules. For example how to compare such field to current date, check if it is equal omitting time, or check if it is date before some time from now?
Drools isn't a real-time program and it doesn't have an innate idea of Time or Now. If you need to investigate relations of some fact property w.r.t. some point of time X, you'll have to establish a fact carrying X as its data, and write your rules based on that.
A more or less coarse approximation of a fact representing Now can be made using timers. You can implement a rule that modifies a fact containing a value representing Time (e.g. java.util.Date) every second, or less frequently.
Blending out the time of the day is something you'll have to do using Java or DRL functions. Alternatively, if it is days you are interested in, use some custom class representing days, with some suitable day 1 defined by you.
you can give like
inputDate>=11-Nov-2014
provide your current date to inputDate rule input Fact variable.
Should I store it in a single timestamp/datetime field or separate date and time fields? I prefer to store it as a single timestamp field but I need to know when a user didn't enter a time portion.
How to best store this in the database? I'm using postgresql.
There are definitely reasons why this is a bad idea. There are also reasons why your choices are limited. It's a bad idea because it's a single data item and for the more practical reason that you can't store a timezone if you have two fields.
As mentioned above, nulls are the obvious benefit of using two fields.
You might also want to consider using a single datetime field and storing a flag to indicate whether or not the user entered a time. This could be a boolean flag. However, you will still need to think about how you are going to use this data - entering only a date into a datetime field will lead to a time component being set to midnight. This will have implications in sorting and selection. Additionally, if you are storing timezones, you will have to be very careful when you use the data.
In order to fulfill your requirement of knowing whether or not a time was entered you will need to have two fields. You do not need the second field to be a time though.
The obvious answer is to use two separate fields; then you can use NULL values.
If you choose to use one field you will need to choose a magic time part that signifies "didn't enter a real time", which has the danger of coinciding with a real time (however unlikely).
Also, if you intend to use the date and time part separately often, then it might also be convenient to use separate fields; otherwise you will often need to use selection functions for extracting the relevant part of a field.