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Is it safe to say that there are two types of variable in Swift ?
variable
Constant
Can constant be reffered to as a type of variable?
I ask this question because in programming world, variable can be define as data container (way to hold and store data).
Need more light shed on this to clear all doubt.
In Swift, a constant and a variable are two different types of data containers that are declared with different keywords, let and var respectively. So a constant is not a type of variable.
A variable is a data container whose value can be changed. A constant is a data container whose value is set once and can never be changed.
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I have been looking around in the documentation, but could not find an explanation of what the "int2vector" type really is. It is found in some system tables like pg_trigger, but that's all a documentation search returns...
It seems to be vaguely similar to int2array, but has a different OID (INT2VECTOROID is 22, INT2ARRAYOID is 1005).
I have found ways to generate int2array in SQL (for instance with SELECT cast('{1,2}' as int2[])), but not int2vector.
The question applies to int4vector & int4array as well, and the uses case is when interfacing with libpq in binary format.
int2vector is an obsolete data type for arrays of smallint from the time before PostgreSQL had array data types. Today you would use smallint[].
You shouldn't use int2vector in your table definitions, as it is not documented. On the other hand, it is unlikely to get removed, since the catalog tables make use of that data type for historical reasons. There is no advantage to be had by using int2vector.
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My app involves repeated equality comparisons of many megabytes of an array of strings. I was (naively?) surprised that such comparisons became immensely faster when I added a shadow array of the count of each string; if the counts are not equal, the strings cannot be equal.
I would have thought that the Swift compiler could easily and efficiently maintain a string's count in the internal representation, and short-circuit string equality comparisons if the counts differ. The initial creation of each string would provide the opportunity to initialize the count, and each manipulation would then know the count of each participant. But it seems not so. If only some applications would benefit from a stored count, a compiler switch to turn it on could help them.
Would this be a reasonable standard library refinement?
The problem with String is that it is not stored always in the same way. There are different types of storage and for them to be properly compared, they have to be converted to the same representation first.
Looking into the source code here: StringComparison.swift, I think you are right and count should be compared first when checking equality.
I recommend filing a bug.
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I am making a use case diagram for a school and was wondering how I can show a degree course is either full time or part time and then each degree contains 1 to 10 courses.
Thanks!
The rules you are giving in your question are not captured in the use case model, but in the domain model. The description of a use case is influenced by the domain model. Like for example a use case enroll for term will describe steps where the user enters one or more courses. For a domain model you would create a class diagram.
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How can I create a member in a PDS using either JCL or REXX? The member's name must contain the actual date. Is that possible?
It can be done in JCL and by Rexx. You need to remember that member names are a maximum of 8 bytes and cannot start with a numeric so you would need to use something like the 'Julian' date e.g. 2017365. You may have system variables available to populate your JCL - check the JCL manual and level of Z/os that you are using.
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I have 3 FirDataSnapshot. When I am using observeEventType(.ChildAdded,..), it returns 3 item. When I use observeSingeEventTypeOf, it returns only 1 snapshot. I don't know why.
observeSingleEventType returns single value means it observe .childAdded only once ... the block is immediately canceled after the initial data is returned.
If you are using observeEventType than it gets all values from database ..