Failure due to memcpy being called at compile time
Steven Schveighoffer
schveiguy at gmail.com
Mon Jun 13 19:59:16 UTC 2022
On 6/13/22 3:48 PM, JG wrote:
> 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");
> }
> ```
>
>
>
Happens in `moveEmplaceImpl` in `core.lifetime`. Somebody is calling that.
https://github.com/dlang/druntime/blob/v2.099.1/src/core/lifetime.d#L2192
No stack trace though, that would actually be nice to have in the CTFE
interpreter.
I imagine if you solved that call, you would get out to a place where it
tries to cast to the actual type and fail there instead.
-Steve
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