Template pattern delegate?

[frame]

On Sunday, 25 October 2020 at 12:02:10 UTC, Ali Çehreli wrote:
> On 10/25/20 4:30 AM, frame wrote:
>> Is there a possibility to write templated code / custom trait 
>> pattern with usage like a delegate?
>> 
>> I have a try-catch block with different types and don't want 
>> to repeat myself in every method again. It's always the same, 
>> just what's tried changes, eg.:
>> 
>> pseudo code:
>> 
>> template myStuff(mixin code)
>> {
>>      try {
>>          code();
>>      }
>>      catch (X e) {
>>          ...
>>      }
>>      catch (Y e) {
>>          ...
>>      }
>>      ...
>> }
>> 
>> static myStuff!({
>>     writeln("...");
>> });
>> 
>
> That's one of my DConf Onlide slides but for a limited use 
> case! :)
>
> int tried(Func, string functionName = __FUNCTION__, string file 
> = __FILE__, size_t line = __LINE__)(Func func) {
>   static if (!is (ReturnType!Func == int)) {
>     pragma(msg, format!"\n%s(%s): Error: %s must return int 
> error code"(file, line, functionName));
>     static assert(false);
>   }
>
>   void printError(T)(T err) {
>     stderr.writefln!"\n%s(%s): Failed to execute %s: %s"(file, 
> line, functionName, err);
>   }
>
>   try {
>     return func();
>
>   } catch (Exception exc) {
>     printError(exc.msg);
>     return 1;
>
>   } catch (Error err) {
>     printError(err);
>     import core.stdc.stdlib : abort;
>     abort();
>   }
>
>   assert(false);
> }
>
> Then, all extern(C) functions would be written the same way:
>
> extern(C) int foo() {
>   return tried({
>     // ...
>     return 0;
>   });
> }
>
> Ali

I see that your approach can handle functions and delegates but 
isn't that not equivalent like this template for a function?

auto myStuff(T)(T function() fn) {
     try {
         return fn();
     }
     catch (Exception e) {
         //
     }
}

I wonder if I could use such a template as static variant and the 
compiler just expands the code? Just thinking that using a 
function or delegate is an overhead. Maybe not a function but a 
delegate will allocate GC memory I think.