Formatting a pointer

{} writes what a pointer points at, and {:p} writes its address; chosen by the user on 2026-10-22 (“if I try to format a ^Person, I want to see the Person … to print the pointer, we could have {:p}”). This reverses the part of D-0080 that said a pointer has no Format, which was a consequence of formatting through &Format rather than a choice (T-0055).

A pointer is written as a reference is, one level down: println!("{}", p) with p: ^Person writes the Person by its own Format, and a spec applies to what it points at, so {:x} of a ^i32 is the integer in hex. A pointer to a pointer is an error whose help says to write p^.
A null pointer is written null, rather than read through. Claude’s call, made while implementing: reading through it would crash the program that is trying to report something.
{:p} is the address, in hex after 0x on every platform (C’s %p differs between libraries), right-aligned in a width as a number is. It suits a pointer only, and a zero fill is refused, since the zeros would land before the 0x.
It is the formatting macros’ doing, not an impl Format for ^T. A trait implemented for a pointer type is not supported (the compiler accepts one and then emits C++ that calls the method on the pointee, T-0080), so a T: Format bound is not satisfied by a pointer. The macros handle a pointer argument themselves, through Formatter::write_pointee and write_address.
error(…) writes a pointer only under {:p}: its message is built without allocating and without Format (§9.2), so it has no way to write what a pointer points at, and {} on one is an error there (DZ0527).

What made it possible is T-0056, done in the same revision: each placeholder is written by a direct call to its argument’s Format::format, so a generic method such as write_pointee<T: Format> needs no vtable (§12.9, r69).