Printing and Formatting

Macros	Return type	Description
@print(fmt, ...)	void	write format to stdout
@println(fmt, ...)	void	write format to stdout with newline
@format(fmt, ...)	String	format values into heap String
@dbg(expr)	expr	debug provided expression (Debug mode only)

Specifiers

Slot	Meaning
{}	value (Display)
{:?}	debug (Debug)
{hex}	hexadecimal
{oct}	octal
{bin}	binary
{:.N}	float with N decimals

Only {:?} and {:.N} are written with a colon, the other specifiers are bare: {hex}, not {:hex}.

Display and Debug

Structs opt in through core.io interfaces. The sink is any StrWriter, so the same code feeds stdout and String:

implement Display : Point {
  fn display[W: StrWriter](*const self, out: *W) void {
    out.write_str("point");
  }
}