> The C++26 draft has not yet had its final ballot
This is co-authored by Bjarne, and so I'm sure it's not trivially false, but maybe I am just missing some detail. I know Bjarne was threatening to cast a veto of C++26 over this, but I thought he did not?
Anyone who follows the process a bit more than me have some context here?
There is a small hint of it at the end, but I really hope compile time contract assertions become more common. I know some languages like spark, dafny and a few others do it and generate implicit contracts for things like divide by 0. I've been experimenting with my own custom language that do these things and going back to c++ every day at work is actually a slight let down because of it.
Suppose your function doodle_widget is supposed to take a Gonzo Widget, but you're worried somebody might call it with a Non-Gonzo Widget and that can't work.
Traditionally you write code which checks the Widget to see if it's Gonzo and if not you throw an exception. Callers can pick, for this function in particular, whether to handle the Exception, in which case they get that Exception to look at, or they can "bubble it up" to be handled in their caller, and so on all the way to the top of the program where if it bubbles up it's reported and then exits the program.
With Contracts you write a contract for the function with a pre-condition that the Widget is Gonzo. Your users (programmers who might call doodle_widget) can pick: If they fail a contract the program exits immediately reporting a violation ("quick enforce"), it reports the violation via a global contract handler and then exits ("enforce") or it just reports to the handler but doesn't exit ("observe") or finally, they ignore it entirely ("ignore")
These just aren't that different. The contract is maybe slightly better because of the enhanced semantic discovery - you could imagine tooling which gives you a yellow squiggly line because your code violates a contract requirement for example, it's definitely not practical to check exception raising that way.
>Suppose your function doodle_widget is supposed to take a Gonzo Widget, but you're worried somebody might call it with a Non-Gonzo Widget and that can't work.
One thing that I'm curious about regarding all of this: I thought all of this stuff landed in C++26, yet we are still getting papers like https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2026/p43...
> The C++26 draft has not yet had its final ballot
This is co-authored by Bjarne, and so I'm sure it's not trivially false, but maybe I am just missing some detail. I know Bjarne was threatening to cast a veto of C++26 over this, but I thought he did not?
Anyone who follows the process a bit more than me have some context here?
There is a small hint of it at the end, but I really hope compile time contract assertions become more common. I know some languages like spark, dafny and a few others do it and generate implicit contracts for things like divide by 0. I've been experimenting with my own custom language that do these things and going back to c++ every day at work is actually a slight let down because of it.
30 years late, but I will take it. Contracts look useful and less messy than exceptions.
They solve completely different problems though
Suppose your function doodle_widget is supposed to take a Gonzo Widget, but you're worried somebody might call it with a Non-Gonzo Widget and that can't work.
Traditionally you write code which checks the Widget to see if it's Gonzo and if not you throw an exception. Callers can pick, for this function in particular, whether to handle the Exception, in which case they get that Exception to look at, or they can "bubble it up" to be handled in their caller, and so on all the way to the top of the program where if it bubbles up it's reported and then exits the program.
With Contracts you write a contract for the function with a pre-condition that the Widget is Gonzo. Your users (programmers who might call doodle_widget) can pick: If they fail a contract the program exits immediately reporting a violation ("quick enforce"), it reports the violation via a global contract handler and then exits ("enforce") or it just reports to the handler but doesn't exit ("observe") or finally, they ignore it entirely ("ignore")
These just aren't that different. The contract is maybe slightly better because of the enhanced semantic discovery - you could imagine tooling which gives you a yellow squiggly line because your code violates a contract requirement for example, it's definitely not practical to check exception raising that way.
>Suppose your function doodle_widget is supposed to take a Gonzo Widget, but you're worried somebody might call it with a Non-Gonzo Widget and that can't work.
Can't you just use concepts?
How do you handle I/O type exceptions with contracts?