initialization of empty structs

[PavelVozenilek]

Copied on request from #548 (comment).

Zig requires initialization, even for empty structs:

const foo = struct {};

pub fn main() -> %void {

  var f : foo;
}

results in :

 
O:\zig0.1.1>zig build-exe b.zig
O:\zig0.1.1\b.zig:11:3: error: variables must be initialized
  var f : foo;
  ^

While empty struct does not make much of sense, asking for its initialization is IMO error.

[andrewrk]

You have 2 options for initializing a struct, whether it has 0 or more fields:

Option 1, recommended, list all the fields in the initializer. With a struct with no fields, there are 0 fields in the initializer. This option is recommended because if you add a field later, you'll get a compiler error here for not initializing all fields.

var f = foo {}; 

Option 2, leave all fields undefined:

var f: foo = undefined;