Struct frame_support::dispatch::fmt::Formatter

pub struct Formatter<'a> { /* fields omitted */ }

Configuration for formatting.

A Formatter represents various options related to formatting. Users do not construct Formatters directly; a mutable reference to one is passed to the fmt method of all formatting traits, like Debug and Display.

To interact with a Formatter, you’ll call various methods to change the various options related to formatting. For examples, please see the documentation of the methods defined on Formatter below.

Implementations

impl<'a> Formatter<'a>

pub fn pad_integral(
    &mut self,
    is_nonnegative: bool,
    prefix: &str,
    buf: &str
) -> Result<(), Error>

Performs the correct padding for an integer which has already been emitted into a str. The str should not contain the sign for the integer, that will be added by this method.

Arguments

• is_nonnegative - whether the original integer was either positive or zero.
• prefix - if the ‘#’ character (Alternate) is provided, this is the prefix to put in front of the number.
• buf - the byte array that the number has been formatted into

This function will correctly account for the flags provided as well as the minimum width. It will not take precision into account.

Examples

use std::fmt;

struct Foo { nb: i32 }

impl Foo {
    fn new(nb: i32) -> Foo {
        Foo {
            nb,
        }
    }
}

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        // We need to remove "-" from the number output.
        let tmp = self.nb.abs().to_string();

        formatter.pad_integral(self.nb >= 0, "Foo ", &tmp)
    }
}

assert_eq!(&format!("{}", Foo::new(2)), "2");
assert_eq!(&format!("{}", Foo::new(-1)), "-1");
assert_eq!(&format!("{}", Foo::new(0)), "0");
assert_eq!(&format!("{:#}", Foo::new(-1)), "-Foo 1");
assert_eq!(&format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");

pub fn pad(&mut self, s: &str) -> Result<(), Error>

This function takes a string slice and emits it to the internal buffer after applying the relevant formatting flags specified. The flags recognized for generic strings are:

• width - the minimum width of what to emit
• fill/align - what to emit and where to emit it if the string provided needs to be padded
• precision - the maximum length to emit, the string is truncated if it is longer than this length

Notably this function ignores the flag parameters.

Examples

use std::fmt;

struct Foo;

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        formatter.pad("Foo")
    }
}

assert_eq!(&format!("{:<4}", Foo), "Foo ");
assert_eq!(&format!("{:0>4}", Foo), "0Foo");

pub fn write_str(&mut self, data: &str) -> Result<(), Error>

Writes some data to the underlying buffer contained within this formatter.

Examples

use std::fmt;

struct Foo;

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        formatter.write_str("Foo")
        // This is equivalent to:
        // write!(formatter, "Foo")
    }
}

assert_eq!(&format!("{}", Foo), "Foo");
assert_eq!(&format!("{:0>8}", Foo), "Foo");

pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<(), Error>

Writes some formatted information into this instance.

Examples

use std::fmt;

struct Foo(i32);

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        formatter.write_fmt(format_args!("Foo {}", self.0))
    }
}

assert_eq!(&format!("{}", Foo(-1)), "Foo -1");
assert_eq!(&format!("{:0>8}", Foo(2)), "Foo 2");

pub fn flags(&self) -> u32

👎 Deprecated since 1.24.0:

use the sign_plus, sign_minus, alternate, or sign_aware_zero_pad methods instead

Flags for formatting

pub fn fill(&self) -> char

Character used as ‘fill’ whenever there is alignment.

Examples

use std::fmt;

struct Foo;

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        let c = formatter.fill();
        if let Some(width) = formatter.width() {
            for _ in 0..width {
                write!(formatter, "{}", c)?;
            }
            Ok(())
        } else {
            write!(formatter, "{}", c)
        }
    }
}

// We set alignment to the right with ">".
assert_eq!(&format!("{:G>3}", Foo), "GGG");
assert_eq!(&format!("{:t>6}", Foo), "tttttt");

pub fn align(&self) -> Option<Alignment>

Flag indicating what form of alignment was requested.

Examples

extern crate core;

use std::fmt::{self, Alignment};

struct Foo;

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        let s = if let Some(s) = formatter.align() {
            match s {
                Alignment::Left    => "left",
                Alignment::Right   => "right",
                Alignment::Center  => "center",
            }
        } else {
            "into the void"
        };
        write!(formatter, "{}", s)
    }
}

assert_eq!(&format!("{:<}", Foo), "left");
assert_eq!(&format!("{:>}", Foo), "right");
assert_eq!(&format!("{:^}", Foo), "center");
assert_eq!(&format!("{}", Foo), "into the void");

pub fn width(&self) -> Option<usize>

Optionally specified integer width that the output should be.

Examples

use std::fmt;

struct Foo(i32);

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        if let Some(width) = formatter.width() {
            // If we received a width, we use it
            write!(formatter, "{:width$}", &format!("Foo({})", self.0), width = width)
        } else {
            // Otherwise we do nothing special
            write!(formatter, "Foo({})", self.0)
        }
    }
}

assert_eq!(&format!("{:10}", Foo(23)), "Foo(23)   ");
assert_eq!(&format!("{}", Foo(23)), "Foo(23)");

pub fn precision(&self) -> Option<usize>

Optionally specified precision for numeric types. Alternatively, the maximum width for string types.

Examples

use std::fmt;

struct Foo(f32);

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        if let Some(precision) = formatter.precision() {
            // If we received a precision, we use it.
            write!(formatter, "Foo({1:.*})", precision, self.0)
        } else {
            // Otherwise we default to 2.
            write!(formatter, "Foo({:.2})", self.0)
        }
    }
}

assert_eq!(&format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
assert_eq!(&format!("{}", Foo(23.2)), "Foo(23.20)");

pub fn sign_plus(&self) -> bool

Determines if the + flag was specified.

Examples

use std::fmt;

struct Foo(i32);

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        if formatter.sign_plus() {
            write!(formatter,
                   "Foo({}{})",
                   if self.0 < 0 { '-' } else { '+' },
                   self.0)
        } else {
            write!(formatter, "Foo({})", self.0)
        }
    }
}

assert_eq!(&format!("{:+}", Foo(23)), "Foo(+23)");
assert_eq!(&format!("{}", Foo(23)), "Foo(23)");

pub fn sign_minus(&self) -> bool

Determines if the - flag was specified.

Examples

use std::fmt;

struct Foo(i32);

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        if formatter.sign_minus() {
            // You want a minus sign? Have one!
            write!(formatter, "-Foo({})", self.0)
        } else {
            write!(formatter, "Foo({})", self.0)
        }
    }
}

assert_eq!(&format!("{:-}", Foo(23)), "-Foo(23)");
assert_eq!(&format!("{}", Foo(23)), "Foo(23)");

pub fn alternate(&self) -> bool

Determines if the # flag was specified.

Examples

use std::fmt;

struct Foo(i32);

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        if formatter.alternate() {
            write!(formatter, "Foo({})", self.0)
        } else {
            write!(formatter, "{}", self.0)
        }
    }
}

assert_eq!(&format!("{:#}", Foo(23)), "Foo(23)");
assert_eq!(&format!("{}", Foo(23)), "23");

pub fn sign_aware_zero_pad(&self) -> bool

Determines if the 0 flag was specified.

Examples

use std::fmt;

struct Foo(i32);

impl fmt::Display for Foo {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        assert!(formatter.sign_aware_zero_pad());
        assert_eq!(formatter.width(), Some(4));
        // We ignore the formatter's options.
        write!(formatter, "{}", self.0)
    }
}

assert_eq!(&format!("{:04}", Foo(23)), "23");

pub fn debug_struct(&'b mut self, name: &str) -> DebugStruct<'b, 'a>

Creates a DebugStruct builder designed to assist with creation of fmt::Debug implementations for structs.

Examples

use std::fmt;
use std::net::Ipv4Addr;

struct Foo {
    bar: i32,
    baz: String,
    addr: Ipv4Addr,
}

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_struct("Foo")
            .field("bar", &self.bar)
            .field("baz", &self.baz)
            .field("addr", &format_args!("{}", self.addr))
            .finish()
    }
}

assert_eq!(
    "Foo { bar: 10, baz: \"Hello World\", addr: 127.0.0.1 }",
    format!("{:?}", Foo {
        bar: 10,
        baz: "Hello World".to_string(),
        addr: Ipv4Addr::new(127, 0, 0, 1),
    })
);

pub fn debug_tuple(&'b mut self, name: &str) -> DebugTuple<'b, 'a>

Creates a DebugTuple builder designed to assist with creation of fmt::Debug implementations for tuple structs.

Examples

use std::fmt;
use std::marker::PhantomData;

struct Foo<T>(i32, String, PhantomData<T>);

impl<T> fmt::Debug for Foo<T> {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_tuple("Foo")
            .field(&self.0)
            .field(&self.1)
            .field(&format_args!("_"))
            .finish()
    }
}

assert_eq!(
    "Foo(10, \"Hello\", _)",
    format!("{:?}", Foo(10, "Hello".to_string(), PhantomData::<u8>))
);

pub fn debug_list(&'b mut self) -> DebugList<'b, 'a>

Creates a DebugList builder designed to assist with creation of fmt::Debug implementations for list-like structures.

Examples

use std::fmt;

struct Foo(Vec<i32>);

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_list().entries(self.0.iter()).finish()
    }
}

assert_eq!(format!("{:?}", Foo(vec![10, 11])), "[10, 11]");

pub fn debug_set(&'b mut self) -> DebugSet<'b, 'a>

Creates a DebugSet builder designed to assist with creation of fmt::Debug implementations for set-like structures.

Examples

use std::fmt;

struct Foo(Vec<i32>);

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_set().entries(self.0.iter()).finish()
    }
}

assert_eq!(format!("{:?}", Foo(vec![10, 11])), "{10, 11}");

In this more complex example, we use format_args! and .debug_set() to build a list of match arms:

use std::fmt;

struct Arm<'a, L: 'a, R: 'a>(&'a (L, R));
struct Table<'a, K: 'a, V: 'a>(&'a [(K, V)], V);

impl<'a, L, R> fmt::Debug for Arm<'a, L, R>
where
    L: 'a + fmt::Debug, R: 'a + fmt::Debug
{
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        L::fmt(&(self.0).0, fmt)?;
        fmt.write_str(" => ")?;
        R::fmt(&(self.0).1, fmt)
    }
}

impl<'a, K, V> fmt::Debug for Table<'a, K, V>
where
    K: 'a + fmt::Debug, V: 'a + fmt::Debug
{
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_set()
        .entries(self.0.iter().map(Arm))
        .entry(&Arm(&(format_args!("_"), &self.1)))
        .finish()
    }
}

pub fn debug_map(&'b mut self) -> DebugMap<'b, 'a>

Creates a DebugMap builder designed to assist with creation of fmt::Debug implementations for map-like structures.

Examples

use std::fmt;

struct Foo(Vec<(String, i32)>);

impl fmt::Debug for Foo {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
    }
}

assert_eq!(
    format!("{:?}",  Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
    r#"{"A": 10, "B": 11}"#
 );

Trait Implementations

impl<'a, 'b> Serializer for &'a mut Formatter<'b>

use serde::Serialize;
use std::fmt::{self, Display};

#[derive(Serialize)]
#[serde(rename_all = "kebab-case")]
pub enum MessageType {
    StartRequest,
    EndRequest,
}

impl Display for MessageType {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.serialize(f)
    }
}

type Ok = ()

The output type produced by this Serializer during successful serialization. Most serializers that produce text or binary output should set Ok = () and serialize into an io::Write or buffer contained within the Serializer instance. Serializers that build in-memory data structures may be simplified by using Ok to propagate the data structure around.

type Error = Error

The error type when some error occurs during serialization.

type SerializeSeq = Impossible<(), Error>

Type returned from serialize_seq for serializing the content of the sequence.

type SerializeTuple = Impossible<(), Error>

Type returned from serialize_tuple for serializing the content of the tuple.

type SerializeTupleStruct = Impossible<(), Error>

Type returned from serialize_tuple_struct for serializing the content of the tuple struct.

type SerializeTupleVariant = Impossible<(), Error>

Type returned from serialize_tuple_variant for serializing the content of the tuple variant.

type SerializeMap = Impossible<(), Error>

Type returned from serialize_map for serializing the content of the map.

type SerializeStruct = Impossible<(), Error>

Type returned from serialize_struct for serializing the content of the struct.

type SerializeStructVariant = Impossible<(), Error>

Type returned from serialize_struct_variant for serializing the content of the struct variant.

pub fn serialize_bool(self, v: bool) -> Result<(), Error>

Serialize a bool value.

pub fn serialize_i8(self, v: i8) -> Result<(), Error>

Serialize an i8 value.

pub fn serialize_i16(self, v: i16) -> Result<(), Error>

Serialize an i16 value.

pub fn serialize_i32(self, v: i32) -> Result<(), Error>

Serialize an i32 value.

pub fn serialize_i64(self, v: i64) -> Result<(), Error>

Serialize an i64 value.

pub fn serialize_u8(self, v: u8) -> Result<(), Error>

Serialize a u8 value.

pub fn serialize_u16(self, v: u16) -> Result<(), Error>

Serialize a u16 value.

pub fn serialize_u32(self, v: u32) -> Result<(), Error>

Serialize a u32 value.

pub fn serialize_u64(self, v: u64) -> Result<(), Error>

Serialize a u64 value.

pub fn serialize_f32(self, v: f32) -> Result<(), Error>

Serialize an f32 value.

pub fn serialize_f64(self, v: f64) -> Result<(), Error>

Serialize an f64 value.

pub fn serialize_char(self, v: char) -> Result<(), Error>

Serialize a character.

pub fn serialize_str(self, v: &str) -> Result<(), Error>

Serialize a &str.

pub fn serialize_unit_struct(self, v: &'static str) -> Result<(), Error>

Serialize a unit struct like struct Unit or PhantomData<T>.

pub fn serialize_i128(self, v: i128) -> Result<(), Error>

Serialize an i128 value.

pub fn serialize_u128(self, v: u128) -> Result<(), Error>

Serialize a u128 value.

pub fn serialize_unit_variant(
    self,
    _name: &'static str,
    _variant_index: u32,
    variant: &'static str
) -> Result<(), Error>

Serialize a unit variant like E::A in enum E { A, B }.

pub fn serialize_newtype_struct<T>(
    self,
    _name: &'static str,
    value: &T
) -> Result<(), Error> where
    T: Serialize + ?Sized, 

Serialize a newtype struct like struct Millimeters(u8).

pub fn serialize_bytes(self, _v: &[u8]) -> Result<(), Error>

Serialize a chunk of raw byte data.

pub fn serialize_none(self) -> Result<(), Error>

Serialize a None value.

pub fn serialize_some<T>(self, _value: &T) -> Result<(), Error> where
    T: Serialize + ?Sized, 

Serialize a Some(T) value.

pub fn serialize_unit(self) -> Result<(), Error>

Serialize a () value.

pub fn serialize_newtype_variant<T>(
    self,
    _name: &'static str,
    _variant_index: u32,
    _variant: &'static str,
    _value: &T
) -> Result<(), Error> where
    T: Serialize + ?Sized, 

Serialize a newtype variant like E::N in enum E { N(u8) }.

pub fn serialize_seq(
    self,
    _len: Option<usize>
) -> Result<<&'a mut Formatter<'b> as Serializer>::SerializeSeq, Error>

Begin to serialize a variably sized sequence. This call must be followed by zero or more calls to serialize_element, then a call to end.

pub fn serialize_tuple(
    self,
    _len: usize
) -> Result<<&'a mut Formatter<'b> as Serializer>::SerializeTuple, Error>

Begin to serialize a statically sized sequence whose length will be known at deserialization time without looking at the serialized data. This call must be followed by zero or more calls to serialize_element, then a call to end.

pub fn serialize_tuple_struct(
    self,
    _name: &'static str,
    _len: usize
) -> Result<<&'a mut Formatter<'b> as Serializer>::SerializeTupleStruct, Error>

Begin to serialize a tuple struct like struct Rgb(u8, u8, u8). This call must be followed by zero or more calls to serialize_field, then a call to end.

pub fn serialize_tuple_variant(
    self,
    _name: &'static str,
    _variant_index: u32,
    _variant: &'static str,
    _len: usize
) -> Result<<&'a mut Formatter<'b> as Serializer>::SerializeTupleVariant, Error>

Begin to serialize a tuple variant like E::T in enum E { T(u8, u8) }. This call must be followed by zero or more calls to serialize_field, then a call to end.

pub fn serialize_map(
    self,
    _len: Option<usize>
) -> Result<<&'a mut Formatter<'b> as Serializer>::SerializeMap, Error>

Begin to serialize a map. This call must be followed by zero or more calls to serialize_key and serialize_value, then a call to end.

pub fn serialize_struct(
    self,
    _name: &'static str,
    _len: usize
) -> Result<<&'a mut Formatter<'b> as Serializer>::SerializeStruct, Error>

Begin to serialize a struct like struct Rgb { r: u8, g: u8, b: u8 }. This call must be followed by zero or more calls to serialize_field, then a call to end.

pub fn serialize_struct_variant(
    self,
    _name: &'static str,
    _variant_index: u32,
    _variant: &'static str,
    _len: usize
) -> Result<<&'a mut Formatter<'b> as Serializer>::SerializeStructVariant, Error>

Begin to serialize a struct variant like E::S in enum E { S { r: u8, g: u8, b: u8 } }. This call must be followed by zero or more calls to serialize_field, then a call to end.

pub fn collect_str<T>(self, value: &T) -> Result<(), Error> where
    T: Display + ?Sized, 

Serialize a string produced by an implementation of Display.

fn collect_seq<I>(self, iter: I) -> Result<Self::Ok, Self::Error> where
    I: IntoIterator,
    <I as IntoIterator>::Item: Serialize, 

Collect an iterator as a sequence.

fn collect_map<K, V, I>(self, iter: I) -> Result<Self::Ok, Self::Error> where
    I: IntoIterator<Item = (K, V)>,
    K: Serialize,
    V: Serialize, 

Collect an iterator as a map.

fn is_human_readable(&self) -> bool

Determine whether Serialize implementations should serialize in human-readable form.

impl<'_> Write for Formatter<'_>

pub fn write_str(&mut self, s: &str) -> Result<(), Error>

Writes a string slice into this writer, returning whether the write succeeded.

pub fn write_char(&mut self, c: char) -> Result<(), Error>

Writes a char into this writer, returning whether the write succeeded.

pub fn write_fmt(&mut self, args: Arguments<'_>) -> Result<(), Error>

Glue for usage of the write! macro with implementors of this trait.