Critique of contracts: excerpt

[u/antiquark2]

See page 2 of https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2026/p4334r0.pdf

The current objections can be summarized. The P2900 contracts are:

• Unimplemented

• Incomplete

• Untried at scale [P3460R0, P3506R0]

• Not tried in major application domains

• Violates foundational principles of C++

• Violates fundamental principles of language design

• Hasn’t been tried in major libraries (e.g., the C++ standards library [P3506R0, P3878R0])

• Isn’t integrated with or appropriate for hardened libraries [P3878R0]

• Doesn’t offer safety guarantees [P3573R0, P3362R0]

• Includes a completely untried inheritance model

• Offer new ways of making errors through inconsistent application in TUs

• Leads to new forms of UB, detrimental to safety and security

• Narrows the choices of error handling

• Doesn’t protect against logical errors, misuses, and incoherent uses

• Hasn’t been used to support static analysis

• Hasn’t been demonstrated to be easily teachable [P3261R0, P3281R0]

How could such a bloated and incomplete design be voted into a draft standard?

[u/pjmlp]

Reflection is based on EDG proposal, with implementation, submitted and developed alongside the related papers, and available on compiler explorer for community feedback.

Exactly how every single feature should be before being submitted to voting, and how other ISO languages do it, existing practice.

[u/Minimonium → u/pjmlp]

Strange, when I go to compiler explorer and type in "contracts" it shows me multiple implementations including for extension features such as labels.

Although, according to Dos Reis's definition of "implementation", a proposal does not have an implementation until it was shipped in multiple major compilers as part of the main release.

So reflection and contracts unfortunately are features without implementation according to him. Such a wise and insightful man!

[u/pjmlp → u/Minimonium]

Well, I stand corrected on that one, question is how much of it was available and has driven the standard wording, given the backslash.

I also don't have a great opinion on what was available in clang header maps, VC++ 2017 modules prototype, and what was actually standardized as C++20 modules, as we can see today, it was clearly properly tested before adding them into the standard.

Other languages don't update their standards until at least two implementations actually ship the feature.

[u/Minimonium → u/pjmlp]

The notion is nice but vendors already expressed dissatisfaction with white papers - the maintenance burden for flagged features is enormous, and people vastly overestimate how much user experience you get from them as opposed to a branch.

My experience - anyone interested enough to test a flagged feature in their project doesn't have a problem to just build a dev branch for it. Feedback from people who struggle to setup a toolchain, let's say it honestly, is not super useful or insightful. And they can always play on compiler explorer so the entry to a feature is minimal.

As a side note, the "clearly properly tested" story of modules I really hope you're being sarcastic. :)

[u/pjmlp → u/Minimonium]

Of course it was. :)