On Friday, July 5, 2019 10:25:10 AM MDT Nick Treleaven via Digitalmars-d- learn wrote: > On Thursday, 4 July 2019 at 11:06:36 UTC, Eugene Wissner wrote: > > static immutable arr = [1, 2]; > > > > You have to spell it out that the data is static. > > Yes, I was wondering why the compiler doesn't statically allocate > it automatically as an optimization.
It would have to be set up to store the literal somewhere else. Certainly, it can't just put it on the stack, because that risks it going out of scope and causing memory problems. It could theoretically be done with some types, but it's more than simply optimizing the code. As it stands, AFAIK, string literals are the only case where you avoid such allocations, and they get put in a particular place in memory for that to work. Something similar would have to be done with any other array literals where allocation was being avoided (save maybe for a case where scope is used and, and the compiler can statically verify that if it put it on the stack, it wouldn't escape the scope). And if I understand correctly what's being done with string literals, it requires that the value be known at compile time, in which case, any array literals with variables or function calls or the like couldn't work that way. Ultimately though, I think that what it comes down to is that rather than the compiler figuring out which array literals it can treat as special, it simply just knows that it can treat string literals that way and does it with them and nothing else. Another thing to consider is that optimizations shouldn't affect the semantics. So, no matter what optimizations the compiler does with array literals, that shouldn't affect whether the function can be @nogc. For it to affect that, it would have to be something that was guaranteed by the language's semantics regardless of whether any optimizations were being done. So, even if an advanced optimizer really did figure out how to avoid the GC allocations, that wouldn't help with @nogc. Rather, it would have to be built into the semantics of the language. - Jonathan M Davis
