Feature request: adding description field to the @return! contract

[alexveden]

Should we consider adding optional text description to @return! contract with explanations when the error can be returned?

[lerno]

Can you explain what you want with an example?

[alexveden]

Something along those lines:

<* 
String checksum 

@return! Error.ARGUMENT "Empty string is not allowed"
@return! MathError.ZERO_DIVISION : "Magic number should be non-zero"
// Old behavior should be preserved
@return! Error.ARGUMENT
@return! Error.ARGUMENT, MathError.ZERO_DIVISION
*>
fn int! checksum(String s, int magic) {
  if (!s) return Error.ARGUMENT?;
  if (magic == 0) MathError.ZERO_DIVISION?;
 
  int sum = 0;
  foreach(c : s) sum += c;

  return sum / magic;
}

And another crazy idea came to my mind. What if we could extract the error message with reflection mechanism from function pointer/signature:

int! csum = checksum("foo", 0);
if (catch err = csum) {
   io::printfn("Error: %s -- %s", err, checksum.strerror(err)); 
   // Or via some builtin / macro
   //io::printfn("Error: %s -- %s", err, @strerror(checksum, err)); 
}
// Prints
Error: ARGUMENT -- Magic number should be non-zero

[alexveden]

With the functionality above, this could be interlinked with #1985

[lerno]

But isn't a description already possible today?

[alexveden]

Indeed it's possible, but it's not in the docs :(

https://c3-lang.org/language-fundamentals/comments/#_top

[lerno]

I added it to the docs now.