1.0.0[][src]Struct std::fmt::Formatter

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

A struct to represent both where to emit formatting strings to and how they should be formatted. A mutable version of this is passed to all formatting traits.

Methods

impl<'a> Formatter<'a>
[src]

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

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");Run

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");Run

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");Run

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

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)
    }
}

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

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)");Run

Optionally specified precision for numeric 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)");Run

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)");Run

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)");Run

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");Run

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");Run

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),
    })
);Run

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>))
);Run

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()
    }
}

// prints "[10, 11]"
println!("{:?}", Foo(vec![10, 11]));Run

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()
    }
}

// prints "{10, 11}"
println!("{:?}", Foo(vec![10, 11]));Run

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()
    }
}Run

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()
    }
}

// prints "{"A": 10, "B": 11}"
println!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)]));Run

Trait Implementations

impl<'_> Write for Formatter<'_>
1.2.0
[src]

Writes a slice of bytes 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

impl<'a> !Send for Formatter<'a>

impl<'a> !Sync for Formatter<'a>

Blanket Implementations

impl<T, U> TryFrom for T where
    T: From<U>, 
[src]

🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from #33417)

Performs the conversion.

impl<T> From for T
[src]

Performs the conversion.

impl<T, U> TryInto for T where
    U: TryFrom<T>, 
[src]

🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from #33417)

Performs the conversion.

impl<T, U> Into for T where
    U: From<T>, 
[src]

Performs the conversion.

impl<T> Borrow for T where
    T: ?Sized
[src]

Important traits for &'_ mut I

Immutably borrows from an owned value. Read more

impl<T> BorrowMut for T where
    T: ?Sized
[src]

Important traits for &'_ mut I

Mutably borrows from an owned value. Read more

impl<T> Any for T where
    T: 'static + ?Sized
[src]

🔬 This is a nightly-only experimental API. (get_type_id #27745)

this method will likely be replaced by an associated static

Gets the TypeId of self. Read more