问题
I'm reading a journal article about Real-Time Concurrent C, and it mentions in the abstract (so any of you can see the context through that link as well) that "Concurrent C, is a parallel superset of C (and of C++)".
Now I know what a superset is, but what do they mean by a "parallel superset" when referring to programming languages?
回答1:
They're claiming two things, not one thing that is "modified". It's like saying "a quick red car"; the car is quick and red, it's not having a fast color.
- It's parallel, because it supports parallel programming
- It's a super-set, because every valid C or C++ program is also a valid Concurrent C program.
That's a bit weird too, since not every valid C program is a valid C++ program.
回答2:
That's two separate concepts.
"Superset" means it extends the language, without removing or changing any existing language features. So any valid C program is (in theory) a valid Concurrent C program.
"Parallel" means that the extensions support parallel execution - programs can do more than one thing at the same time.
回答3:
This article is old. It was written in some previous millennium. It predates the first C++ standard and the first release of the realtime extension to POSIX.
While C++ existed conceptually back then, there was no way to say what C++ was. There was no C++ standard, de facto or official, in 1991. Nowadays, there is a C++ standard.
C++ has not officially supported parallelism until very recently. POSIX extends C rather than C++, and strictly speaking, it is not a superset; it conflicts with the C standard in key areas. The same applies to Microsoft extensions to C/C++.
In my opinion, the first parallel supersets of ISO/IEC 9899 and ISO/IEC 14882, are C11 and C++11, and strictly speaking, even those are not supersets. They extend C/C++ in some areas, but restrict it in others (e.g., restrict, which wasn't a keyword in the original C standard).
来源：https://stackoverflow.com/questions/30378080/what-does-it-mean-when-one-language-is-a-parallel-superset-of-another