Discussion Thread: DIP 1029--Add throw as Function Attribute--Final Review

[NaN]

On Saturday, 18 April 2020 at 12:03:46 UTC, Jacob Carlborg wrote:
> On 2020-04-17 13:28, Mike Parker wrote:
>> This is the discussion thread for the Final Review of DIP 
>> 1029, "Add throw as Function Attribute":
>> 
>> https://github.com/dlang/DIPs/blob/9db80ddadcf5a220958ddcfec14b9c71cdb43d1c/DIPs/DIP1029.md
>
> I would like to see the "throw" keyword being used as an 
> attribute to implement something like "Zero-overhead 
> deterministic exceptions: Throwing values" [1].
>
> I imagine it looking something like this:
>
> enum CopyError
> {
>     permissionDenied
> }
>
> void copy(string src, string dest) throw(CopyError)
> {
>     throw CopyError.permissionDenied;
> }
>
> void main()
> {
>     try
>         copy("foo", "bar");
>     catch (CopyError e)
>         writeln(e);
> }
>
> Which would be lowered to something like the equivalent of the 
> following code:

You could have the caller pass an alternate return address to the 
callee. So...

void copy(string src, string dest, void* err)
{
     if (somethingbad) { EAX = errorcode; RET (to) err; } ***
}

void main()
{
     auto result = copy("foo", "bar", &L1);

     return;

     L1: writeln("Oh noes!");
}

*** So all the callee has to do is poke the alternate return 
address into the stack and RET as normal. (On x86 at least).