I do not know these constructs, sorry.
Is this similar to pascals "with"?:

with a do begin
 b=1;
 c=2;
 d=3;
end;

Anyway this is too advanced for me I would not write this and I have nowhere read this until now. ;-/

struct a {
  int b {};
  int c {};
  int d {};
};

a = { 1, 2, 3 };

a = { .b = 1, .c = 2, .d = 3 };