Comment by atmikemikeb

I thought about dynamically sized types (DSTs) in zig recently. Was considering writing about it. I came to a different conclusion. Why not use zig's opaque?

It's pretty clean at this imo: Less metaprogramming but I think nicer to use in some cases.

  const Connection = opaque {
    pub const Header = struct {
      host_len: usize,
      // add more static fields or dynamic field lengths here
      //buff_len: usize,
    };

    pub fn init(a: std.mem.Allocator, args: struct { host: []const u8 }) *@This() {
      var this = a.allocWithOptions(u8, @sizeOf(Header) + host.len, @alignOf(Header), null);
      @memcpy(this[@sizeOf(Header)..], host);
      return this.ptr; 
    }

    pub fn host(self: *const @This()) []const u8 {
      const bytes: *u8 = @ptrCast(self);
      const header: *Header = @ptrCast(self);
      const data = bytes[@sizeOf(Header)..];
      const host = data[0..header.host_len];
      return host;
    }
  };

going off memory so I expect it to not actually compile, but I've definitely done something like this before.