Trait WriteMarker

Source

pub trait WriteMarker {
    type Kind;
    type This: ?Sized;
}

Expand description

Marker trait for types that can be written into.

§Implementors

Types that implement this trait are also expected to implement these inherent methods:

// use const_format::{FormattingFlags, Formatter};

const fn borrow_mutably(&mut self) -> &mut Self
const fn make_formatter(&mut self, flags: FormattingFlags) -> Formatter<'_>

§Coercions

The Kind and This associated types are used in the IsAWriteMarker marker type to convert a &mut StrWriter<_> to a StrWriterMut<'_>, and leave other mutable references unconverted.

§Example

Implementing this trait for a String-like inline allocated type.


use const_format::marker_traits::{IsNotAStrWriter, WriteMarker};
use const_format::{Formatter, FormattingFlags};
use const_format::writec;

mod arraystring {
    use const_format::marker_traits::{IsNotAStrWriter, WriteMarker};
    use const_format::{Formatter, FormattingFlags};

    const ARRAY_CAP: usize = 64;
    pub struct ArrayString  {
        len: usize,
        arr: [u8; ARRAY_CAP],
    }
    
    impl WriteMarker for ArrayString  {
        type Kind = IsNotAStrWriter;
        type This = Self;
    }
    
    impl ArrayString {
        pub const fn new() -> Self {
            Self { len: 0, arr: [0; ARRAY_CAP] }
        }
         
        // Gets the part of the array that has been written to.
        pub const fn as_bytes(&self) -> &[u8] {
            const_format::utils::slice_up_to_len_alt(&self.arr, self.len)
        }
    
        pub const fn borrow_mutably(&mut self) -> &mut Self {
            self
        }
    
        pub const fn make_formatter(&mut self, flags: FormattingFlags) -> Formatter<'_> {
            Formatter::from_custom(&mut self.arr, &mut self.len, flags)
        }
    }
}
use arraystring::ArrayString;


let mut buffer = ArrayString::new();

writec!(buffer, "{:?}", [3u8, 5])?;
assert_eq!(buffer.as_bytes(), b"[3, 5]");

writec!(buffer, "{}{:b}", "Hello, world!", 100u16)?;
assert_eq!(buffer.as_bytes(), b"[3, 5]Hello, world!1100100");