How to fix this?

struct S
{
	string[] s;
}

auto foo(string[] s...)   // Error: typesafe variadic function parameter `s` of type `string[]` cannot be marked `return`
{
	return S(s);
}

void main()
{
	import std.stdio: writeln;

	writeln(foo("Hello D"));
}

This successfully compiles with dmd 2.099.1 but fails with 2.100.0

I tried to add return/ref but no luck.

On Tuesday, 24 May 2022 at 22:46:55 UTC, Andrey Zherikov wrote:

return S(s.dup);

The variadic lives in a temporary array that expires at the end of the function. So copying it out to the GC lets it live on.

Your code was wrong on 2.099 too, but the compiler didn't tell you.

On Tuesday, 24 May 2022 at 22:51:50 UTC, Adam Ruppe wrote:

That works, thank you!

Can this error message be improved some way so this fix becomes obvious?

On 5/24/22 6:54 PM, Andrey Zherikov wrote:

What is happening is that you have an auto return function, which infers attributes.

The parameter is being returned, which means it infers return on the parameter. Then decides that it's not legal.

The compiler error message should be more specific about inferred attribute errors and why they occurred, because they are super-confusing.

I believe there are some recent gains in this space. But it's not 100% yet.

-Steve