Tracking Issue for simple_fmt #105054

Feature gate: #![feature(simple_fmt)]

This is a tracking issue for the simple_fmt method on the Display format trait.

Public API

  pub trait Display {
      fn fmt(&self, f: &mut Formatter) -> Result;
+     fn simple_fmt(&self, f: &mut Formatter) -> Result {
+         self.fmt(f)
+     }
  }

Formatting placeholders without any options, like in format_args!("{}", x), will call the simple_fmt method rather than fmt. This allows for optimized implementations for e.g. <String as Display>::simple_fmt that do not need to pull in code for padding, etc. See #104525 (comment).

Steps / History

• Implementation: Optimize format_args placeholders without options: Display::simple_fmt #104525
• Final comment period (FCP)
• Stabilization PR

Unresolved Questions

• Do we want this on the other formatting traits too? Or only Display?
• Do we want to stabilize this at all, to allow crates to override simple_fmt for their own types?
• Should the method be unsafe, such that the implementation may unsafely assume that the Formatter's options are all set to default?