The trap of capturing by reference when you shouldn't

I have recently investigated a bug where it would sometimes crash the application and sometimes it would not, the bug did seem pretty random at first. After compiling the code with ASAN the report was rather puzzling as it was trying to write to a variable from a function way down the call stack, as it turns out the issue has been a lambda that captured variables by reference, given the callback invocation can sometimes be delayed it was not directly visible to why it would sometimes crash and sometimes not, but as we know when the function goes out of scope the variable will be dead. After I figured out the issue I was wondering how I could prevent anyone from ever passing such a lambda again without forcing anyone to actually read any comments and just have the compilation fail, I mean who reads comments, typically users just copy paste what is already there and slightly modify it as needed, after a bit of thinking and trial and error I came up with following solution https://godbolt.org/z/dj4Ghfe9z, it does require C++20 as it is using concepts. So I thought I'll share it here and perhaps someone has a cleaner way to achieve the same.

TLDR: Concept that prevents passing lambdas that captures references to make callback driven APIs safer.

I also sort of wish that we just could have an attribute or already built-in concepts, a function like sort could annotate the predicate as immediate invocation promising that the call will happen immediately, or perhaps an attribute that states its a deferred invocation in where the compiler should perhaps throw a compile error when references are captured, it's definitely one of those things where I feel like more support from the compiler would be great to avoid shooting yourself in the foot, there are too many ways which is unfortunate.

https://redd.it/1odkilk
@r_cpp