Crate custom_format

This crate extends the standard formatting syntax with custom format specifiers, by providing custom formatting macros.

It uses : (a space and a colon) as a separator before the format specifier, which is not a syntax currently accepted and allows supporting standard specifiers in addition to custom specifiers.

This library comes in two flavors, corresponding to the following features:

• compile-time

  The set of possible custom format specifiers is defined at compilation, so invalid specifiers can be checked at compile-time. This allows the library to have the same performance as when using the standard library formatting traits. See the compile_time::CustomFormat trait.

• runtime

  The formatting method dynamically checks the format specifier at runtime for each invocation. This is a slower version, but has a lower MSRV for greater compatibility. See the runtime::CustomFormat trait.

Additional features

By default, the syn crate is used for parsing arguments of the procedural macros.

To improve compilation time, a fast parsing mode is available when disabling default features. It doesn’t parse the full expression of the arguments, but instead only separate the arguments by the , token when not in a delimited group.

This works for 99% of cases but cannot parse correctly expressions containing commas inside turbofishs or closures without delimiters:

// Compilation error due to incorrect parsing
cfmt::println!("{ :?}", |a, b| a);
cfmt::println!("{:?}", HashMap::<u32, u32>::new());

The workaround is simply to add an additional delimited group, or to define a new variable:

// No compilation error

cfmt::println!("{ :?}", (|a, b| a)); // if a custom specifier is defined
cfmt::println!("{:?}", (HashMap::<u32, u32>::new()));
cfmt::println!("{:?}", { HashMap::<u32, u32>::new() });

let map = HashMap::<u32, u32>::new();
cfmt::println!("{map:?}");
cfmt::println!("{map:?}", map = map);

Modules

compile_time

Provides types associated to compile-time formatting.

runtime

Provides types associated to runtime formatting.

Macros

custom_formatter

Helper macro for constructing a new CustomFormatter value from a format specifier