Note that the mention of Zig that I responded to was in reference to Tony Hoare's "billion dollar mistake", which was making null a valid value of a pointer type, not free after use, which is a quite different issue. As I noted, the mistake doesn't occur in Zig because null is not a valid value for a pointer, only an optional pointer, which must be unwrapped with an explicit null test.
I do think it's a bit too easy to forget a deferred free, although it's possible for tools to detect them. Unfortunately Andrew Kelley is prone to being extremely opinionated about language design (GingerBill is another of that sort) and so macros are forever banned from Zig, but macros are the only mechanism for encapsulating a scoped feature like defer.
