Expand description
C structs as warp maps (card wasmtime-ffi): a struct a header defines (wasmtime_instance_t {uint64_t store_id; size_t __private;}) has a layout by the C rules of LP64 platforms; a call writes a map into its bytes and reads
them back as one. Numbers are numbers, pointers handle ids, arrays lists, nested structs and unions maps (a union
read back holds each of its members, the same bytes seen as each). A layout travels as text, so an executable
carries it with the C function: {store_id:u64,__private:u64}, a union in <…>, an array [u8;16], a pointer
ptr; a field without a name is an anonymous member (C11), its fields the struct’s own