Yes, Rust picked the better default and D is too mature to change it now, unfortunately. Likewise with "pure", "const", and maybe even "nothrow" and "nogc".

However, I don't think it is such a big deal, since you can patch it quite well. Mark your main function as @safe and you are force to make everything @safe (or @trusted as a workaround). The type checker will tell you where to look next.

It is interesting that Rust functions are not pure by default. I guess (did not follow the design discussions), because purity is too limiting. D came up with the concept of "weakly pure", which is useful and strong enough. Also you need transitive const to turn a weakly pure into really pure function.

From long, long ago https://news.ycombinator.com/item?id=6940624

By default, D has no safeguards to prevent you from doing memory-unsafe things, and afaik no compile-time checks short of marking your main method as @safe. However, because the language is by default memory managed, it is fairly easy to stick to safe code without this by avoiding pointer/cast voodoo.

Fortunately with array bounds checks and default initialized variables, memory corruptions aren't very common in D.