Printing is handled by a series of macros defined in std::fmt some of which include:

• format!: write formatted text to String
• print!: same as format! but the text is printed to the console (io::stdout).
• println!: same as print! but a newline is appended.
• eprint!: same as format! but the text is printed to the standard error (io::stderr).
• eprintln!: sames as eprint!but a newline is appended.

All parse text in the same fashion. A plus is that the formatting correctness will be checked at compile time.

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std::fmt contains many traits which govern the display of text. The base form of two important ones are listed below:

• fmt::Debug: Uses the {:?} marker. Format text for debugging purposes.
• fmt::Display: Uses the {} marker. Format text in a more elegant, user friendly fashion.

Here, fmt::Display was used because the std library provides implementations for these types. To print text for custom types, more steps are required.

• Fix the two issues in the above code (see FIXME) so that it runs without error.
• Add a println! macro that prints: Pi is roughly 3.142 by controlling the number of decimal places shown. For the purposes of this exercise, use let pi = 3.141592 as an estimate for Pi. (Hint: you may need to check the std::fmt documentation for setting the number of decimals to display)

std::fmt, macros, struct, and traits