Struct serde::lib::fmt::Formatter

1.0.0 · source · []
pub struct Formatter<'a> {
    flags: u32,
    fill: char,
    align: Alignment,
    width: Option<usize>,
    precision: Option<usize>,
    buf: &'a mut (dyn Write + 'a),
}
Expand description

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.

Fields

flags: u32fill: charalign: Alignmentwidth: Option<usize>precision: Option<usize>buf: &'a mut (dyn Write + 'a)

Implementations

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");

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

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

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");
👎 Deprecated since 1.24.0:

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

Flags for formatting

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!("{Foo:G>3}"), "GGG");
assert_eq!(&format!("{Foo:t>6}"), "tttttt");

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");

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)");

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)");

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)");

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)");

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");

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");

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),
    })
);

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>))
);

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]");

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()
    }
}

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

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)
    }
}

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. Read more

The error type when some error occurs during serialization.

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

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

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

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

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

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

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

Serialize a bool value. Read more

Serialize an i8 value. Read more

Serialize an i16 value. Read more

Serialize an i32 value. Read more

Serialize an i64 value. Read more

Serialize a u8 value. Read more

Serialize a u16 value. Read more

Serialize a u32 value. Read more

Serialize a u64 value. Read more

Serialize an f32 value. Read more

Serialize an f64 value. Read more

Serialize a character. Read more

Serialize a &str. Read more

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

Serialize an i128 value. Read more

Serialize a u128 value. Read more

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

Serialize a newtype struct like struct Millimeters(u8). Read more

Serialize a chunk of raw byte data. Read more

Serialize a None value. Read more

Serialize a Some(T) value. Read more

Serialize a () value. Read more

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

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. Read more

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. Read more

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. Read more

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. Read more

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. Read more

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. Read more

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. Read more

Serialize a string produced by an implementation of Display. Read more

Collect an iterator as a sequence. Read more

Collect an iterator as a map. Read more

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

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

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

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

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.