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- Hacker News
- I'm looking forward to seeing where these go in the future. Can solvers prove my code correct (at least in some trivial cases)? What should happen in a unit test (sometimes I want to test that my program handles out of range values, sometimes it is expensive top check and so I put the contract in to avoid the check at runtime...) Can/should the optimizer account for contracts (same question as unit tests).by bluGill
- Maybe just me, but huge complicated languages like C++ seem as unappealing as ever.
If I’m going to write code by hand, the requirement for a beautiful pleasant language is bigger than ever.
by randyrand - Where do I put these?
If I put them in the header, I have to include half the world because I can't forward declare `Foo foo` argument if I want to check `foo.size() > 3` or similar in a pre/post-condition. This is a non-starter, keeping headers lean is the only way to not end up with 1 hour compiles.
If I put them in the cpp, they lose their only advantage over asserts - that they also double as documentation in the headers.
Did we add 50 pages to the standard for a slightly fancier assert? I feel like this could've been one builtin and a footnote:
contract_assert(expr) - if expr evaluates to false, the behavior of the program is undefined. Implementations are encouraged to emit a runtime check for this in debug builds, or a compiler error in cases where they can statically determine, that the assert will fail.
by nananana9 - The article makes no mention of optimisation use cases. In case anyone already knows off the top of their heads and before I start digging for the answer, is part of the intent here for these to inform the optimiser stages, perhaps similarly to what the if (!(some_condition)) { __builtin_unreachable(); } idiom can achieve?by tsukikage
- Random tidbit: I wrote a GCC compiler plugin years ago to add Contracts to C/C++ while waiting for this to make it into the standard
https://gavinray97.github.io/blog/adding-invariant-to-cpp-de...
The post turned out to be more useful for an intro to writing GCC plugins than anything, but at least I had fun
by gavinray - This reminds me the "Design by Contract" concept from Eiffel programming language:
https://en.wikipedia.org/wiki/Design_by_contract
https://www.eiffel.com/values/design-by-contract/introductio...
by ZuLuuuuuu - I used to be a big fan of contracts, and even implemented it in the Zortech C++ compiler back in the 90's:
https://www.digitalmars.com/ctg/contract.html
I implemented it in D as well. But, it just turned out to not be very useful.
by WalterBright - I don't like it.
I'm all for signing up for a contract if it can turn a runtime error into a compile time error. However, this looks like it just makes more runtime errors. At that point, these seem no better than `assert` except for the fact that they promise to really assert (probably).
The article also points out a big problem which is "Importantly, this aspect of Contracts is why contract assertions must not be used for error handling and input validation: If a function has in-contract requirements to report certain events as errors, that handling must be done with standard C++ control statements that are not optional, never with contract assertions."
That sort of muddy definition of what contracts are supposed to be used for is almost certainly going to make a mess. It's not input validation, but parameter validation.. but not really validation but rather checks which error out, but it's not errors we are producing.
by cogman10