fmt_adapter

This crate provides newtype adaptors to and from any formatting trait. More specifically, it allows one to wrap a value into a filter wrapper which filters out the implementations of all formatting traits except for one and then wrap it into a adaptor wrapper which implements one specific formatting trait, which can be different from the original formatting trait. This is better demonstrated with an example:

// Let's create an example type...
#[derive(Copy, Clone, Debug)]
enum Sign {
    Positive,
    Negative
}
//...and implement a formatting trait by hand.
impl fmt::Display for Sign {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}",
            match self {
                Positive => '+',
                Negative => '-'
            }
        )
    }
}

let sign = Sign::Positive;
println!("The sign character is {}", sign); // Outputs the Display formatting
println!("The sign debug form is {:?}", sign); // Outputs the derived Debug formatting
let sign = DebugFromDisplay(sign); // Wrap it into a formatting adapter
println!("The sign debug form is {:?}", sign); // Outputs the Display formatting, even
                                               // though we have {:?} as the formatting mode
let sign = UpperHexFromDebug(sign.0); // Get the value from the previous adapter
                                      // and do something very random
println!("The sign in uppercase hexadecimal is `0x{:X}`", sign);

All adapters in the crate are generated from a list of traits using a build script. As such, no manual editing of the adaptor delarations and their impl blocks is possible. The generated files are listed in .gitignore — use cargo download and build the crate if you want to explore the generated results, or simply take a look at the build.rs file.

The crate is #![no_std], meaning that it works in a freestanding context and only depends on core::fmt, which requires a functional global allocator.

Types of adapters

Here's a list of adapter types (values between {} can be replaced by any formatting trait):

• Only{trait} — filters out all formatting traits of a type except for {trait}. This can be used to restrict access to formatting traits when transferring objects between subsystems.
• {out_tr}From{in_tr} — implements {out_tr} by using the results of formatting with {in_tr}. This can be used to provide arbitrary formatting methods to interfaces which only accept one specific formatting method while still correctly implementing other formatting traits exactly as specified by the fmt documentation.