Failure due to memcpy being called at compile time

[JG]

Hi,

I reduced my code to the following.  Could anyone help me to 
discover why the line marked with //THIS LINE

causes memcpy to be called, and how can I avoid this?


```d
import std;

struct ParseError { string msg; }

alias ParseErrorOr(T) = SumType!(ParseError,T);
auto parseErrorOr(T)(T x) { return ParseErrorOr!T(x); }

auto parserOr(I,fs...)(I i) {
   alias RetType = typeof(fs[0](I.init));
   auto cur = RetType(ParseError.init);
   foreach(f;fs) {
     if(cur.match!((ParseError e)=>false,_=>true)) { return cur; }
     cur = f(i); //THIS LINE
   }
   return cur;
}

auto parseNothing(I)(I i) {
     return parseErrorOr(tuple(i[0..0],i));
}

void main()
{
     enum a = 
parserOr!(string,parseNothing!string,parseNothing!string)("hello");
}
```