Anonymous struct/tuple/array is a convenience feature that can only be used for values.

Consider the above code without it:

  std.debug.print("hello world!\n", struct{}{});

Now add a value:

  std.debug.print("{}!\n", struct{string: []const u8}{ .string = "hello world"});

Quite unwieldy. Zig used to have variadic functions and it was difficult to work with, complicated metaprogramming, and made how things work less obvious during reading. It was also pretty much only ever used for the "print" function.

> so it's not a type safe language if they use anonymous struct everywhere

It's compile-time checked. The example shows a compile time error when the struct fields are not completed by the anonymous struct

printf in C makes use of variadic arguments (man 3 stdarg) which Zig does not allow (unless you are using a C function) for safety reasons.