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Or just do it in C.

  #define span(T) struct span_##T { size_t len; T *data; }
  #define span_access(T, x, i) (*({              \
    span(T) *_v = (x);                           \
    auto _i = (i);                               \
    if (((size_t)_i) >= _v->len) abort();        \
    &_v->data[_i];                               \
  }))

https://godbolt.org/z/TvxseshGc

nananana9 2 months ago [ - ]

Still requires a gcc/clang specific extension (although this one I'd be very happy to see standardized)

uecker 2 months ago [ - ]

Only statement expressions, but one can also implement this without them.

nananana9 a month ago [ - ]

Still, please standardize them :).

I don't use much C but if you add them to the standard they'll probably trickle down to C++ compilers by 2045 and I'll have a good 10 years to use them before I retire.

uecker a month ago [ - ]

You are not happy with immediately invoked lambda expressions?

nananana9 a month ago [ - ]

Well, I'll take them over the nothing you're giving me :D

But in all seriousness, I want this:

  struct Result { int value; int err; };
  #define TRY(res) \
    ({ \
       Result _res = res; \
       if (failed(res)) return res; \
       res.value; \
    })
  Result f1(...) { ... }
  Result f2() {
     int res = TRY(f1(...)); // <<<<
     ...
     return success();
  }

Can't be done with lambdas since the macro needs to return out of the actual function, not the lambda. Pretty much rust question mark, but without rust, or zig "try" but without zig.

uecker a month ago [ - ]

I see, thanks! There is general consensus that statement expressions should become part of ISO C, but some lack of time to get it done. I am not part of WG21 though, so can't say anything about C++.

fuhsnn 2 months ago [ - ]

The fact that pointer types can't be used with this pattern without typedef still seems kinda primitive to me.

uecker 2 months ago [ - ]

You can use pointer types by using a typedef first, but I agree this not nice (I hope we will fix this in future C). But then, I think this is a minor inconvenience for having an otherwise working span type in C.