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:
With the compile-time feature, 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.
With the runtime feature, 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.
compile-time feature```rust use customformat::compiletime as cfmt; use customformat::customformatter;
use core::fmt;
pub struct DateTime { year: i32, month: u8, month_day: u8, hour: u8, minute: u8, second: u8, nanoseconds: u32, }
macrorules! implcustomformatfor_datetime { (match spec { $($spec:literal => $func:expr $(,)?)* }) => { $( impl cfmt::CustomFormat<{ cfmt::spec($spec) }> for DateTime { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { ($func as fn(&Self, &mut fmt::Formatter) -> fmt::Result)(self, f) } } )* }; }
implcustomformatfordatetime!(match spec { // Year with pad for at least 4 digits "%Y" => |this, f| write!(f, "{:04}", this.year), // Year % 100 (00..99) "%y" => |this, f| write!(f, "{:02}", (this.year % 100).abs()), // Month of the year, zero-padded (01..12) "%m" => |this, f| write!(f, "{:02}", this.month), // Day of the month, zero-padded (01..31) "%d" => |this, f| write!(f, "{:02}", this.monthday), // Hour of the day, 24-hour clock, zero-padded (00..23) "%H" => |this, f| write!(f, "{:02}", this.hour), // Minute of the hour (00..59) "%M" => |this, f| write!(f, "{:02}", this.minute), // Second of the minute (00..60) "%S" => |this, f| write!(f, "{:02}", this.second), // Nanosecond (9 digits) "%9N" => |this, f| write!(f, "{:09}", this.nanoseconds), // Date (%m/%d/%y) "%D" => { |this, f| { let month = customformatter!("%m", this); let day = customformatter!("%d", this); let year = customformatter!("%y", this); write!(f, "{}/{}/{}", month, day, year) } } // The ISO 8601 date format (%Y-%m-%d) "%F" => { |this, f| { let year = customformatter!("%Y", this); let month = customformatter!("%m", this); let day = customformatter!("%d", this); write!(f, "{}-{}-{}", year, month, day) } } // 24-hour time (%H:%M:%S) "%T" => { |this, f| { let hour = customformatter!("%H", this); let minute = customformatter!("%M", this); let second = customformatter!("%S", this); write!(f, "{}:{}:{}", hour, minute, second) } } });
let datetime = DateTime { year: 1836, month: 5, monthday: 18, hour: 23, minute: 45, second: 54, nanoseconds: 123456789, };
// Expands to: // // match (&(datetime), &("The date time is")) { // (arg0, arg1) => { // ::std::println!( // "{0}: {1}-{2}-{3} {4}:{5}:{6}.{7}", // arg1, // ::customformat::customformatter!("%Y", arg0), // ::customformat::customformatter!("%m", arg0), // ::customformat::customformatter!("%d", arg0), // ::customformat::customformatter!("%H", arg0), // ::customformat::customformatter!("%M", arg0), // ::customformat::customformatter!("%S", arg0), // ::customformat::customformatter!("%9N", arg0) // ) // } // }; // // Output: "The date time is: 1836-05-18 23:45:54.123456789" // cfmt::println!( "{1}: {0 :%Y}-{0 :%m}-{0 :%d} {0 :%H}:{0 :%M}:{0 :%S}.{0 :%9N}", datetime, "The date time is" );
// Compile-time error since "%h" is not a valid format specifier // cfmt::println!("{0 :%h}", date_time); ```
runtime feature```rust use custom_format::runtime::{self as cfmt, CustomFormat, CustomFormatter};
use core::fmt;
pub struct DateTime { year: i32, month: u8, month_day: u8, hour: u8, minute: u8, second: u8, nanoseconds: u32, }
impl CustomFormat for DateTime { fn fmt(&self, f: &mut fmt::Formatter, spec: &str) -> fmt::Result { match spec { // Year with pad for at least 4 digits "%Y" => write!(f, "{:04}", self.year), // Year % 100 (00..99) "%y" => write!(f, "{:02}", (self.year % 100).abs()), // Month of the year, zero-padded (01..12) "%m" => write!(f, "{:02}", self.month), // Day of the month, zero-padded (01..31) "%d" => write!(f, "{:02}", self.month_day), // Hour of the day, 24-hour clock, zero-padded (00..23) "%H" => write!(f, "{:02}", self.hour), // Minute of the hour (00..59) "%M" => write!(f, "{:02}", self.minute), // Second of the minute (00..60) "%S" => write!(f, "{:02}", self.second), // Nanosecond (9 digits) "%9N" => write!(f, "{:09}", self.nanoseconds), // Date (%m/%d/%y) "%D" => { let month = CustomFormatter::new("%m", self); let day = CustomFormatter::new("%d", self); let year = CustomFormatter::new("%y", self); write!(f, "{}/{}/{}", month, day, year) } // The ISO 8601 date format (%Y-%m-%d) "%F" => { let year = CustomFormatter::new("%Y", self); let month = CustomFormatter::new("%m", self); let day = CustomFormatter::new("%d", self); write!(f, "{}-{}-{}", year, month, day) } // 24-hour time (%H:%M:%S) "%T" => { let hour = CustomFormatter::new("%H", self); let minute = CustomFormatter::new("%M", self); let second = CustomFormatter::new("%S", self); write!(f, "{}:{}:{}", hour, minute, second) } // Invalid format specifier _ => Err(fmt::Error), } } }
let datetime = DateTime { year: 1836, month: 5, monthday: 18, hour: 23, minute: 45, second: 54, nanoseconds: 123456789, };
// Expands to: // // match (&(datetime), &("The date time is")) { // (arg0, arg1) => { // ::std::println!( // "{0}: {1}-{2}-{3} {4}:{5}:{6}.{7}", // arg1, // ::customformat::CustomFormatter::new(arg0, "%Y"), // ::customformat::CustomFormatter::new(arg0, "%m"), // ::customformat::CustomFormatter::new(arg0, "%d"), // ::customformat::CustomFormatter::new(arg0, "%H"), // ::customformat::CustomFormatter::new(arg0, "%M"), // ::customformat::CustomFormatter::new(arg0, "%S"), // ::customformat::CustomFormatter::new(arg0, "%9N") // ) // } // } // // Output: "The date time is: 1836-05-18 23:45:54.123456789" // cfmt::println!( "{1}: {0 :%Y}-{0 :%m}-{0 :%d} {0 :%H}:{0 :%M}:{0 :%S}.{0 :%9N}", date_time, "The date time is" );
// Panic at runtime since "%h" is not a valid format specifier // cfmt::println!("{0 :%h}", date_time); ```
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