Printable.to_format sometimes doesn't work properly

[LukyGuyLucky]

It was not a single time I encountered that a type implements Printable interface with to_format & to_string method sometimes doesn't produce the same proper result as expected.For below sample,to_string works as expected while to_format doesn't.But I have found several examples in the c3c-master package really works that an UDT implements Printable.to_format.I have no clue what I was missing or doing wrong.

Any help would be appreciated.

import std::io;

fn void main()
{
    io::printn("iterating...");
    test();
}

fn void test()
{
    Person tom={18,"Tom"};
    ImportantPerson luckyMan={.name="Lucky man",.age=26,.title="Bring good luck to everyone"};
  
    Printable[*] team={&tom,&luckyMan};
    foreach(member:team)
    {
        print_person(member);
    }
}

struct Person(Printable)
{
    char age;
    String name;
}

fn usz! Person.to_format(&self,Formatter* f) @dynamic
{
    return f.printf("Person{%s,%s},self.name,self.age");
}
/*
fn String Person.to_string(&self,Allocator allocator=allocator::temp()) @dynamic
{
    return string::tformat("Person{%s,%s}",self.name,self.age);
}
*/

struct ImportantPerson(Printable)
{
    inline Person person;
    String title;
}

fn usz! ImportantPerson.to_format(&self,Formatter* f) @dynamic
{
    return f.printf("ImportantPerson{%s,%s,%s},self.name,self.age,self.title");
}
/*
fn String ImportantPerson.to_string(ImportantPerson* self,Allocator allocator=allocator::temp()) @dynamic
{
    return string::tformat("ImportantPerson{%s,%s,%s}",self.name,self.age,self.title);
}
*/

fn void print_person(Printable p)
{
    io::printn(p);
}