1 // Copyright 2013-2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Utilities for formatting and printing strings
13 #![stable(feature = "rust1", since = "1.0.0")]
17 use cell::{Cell, RefCell, Ref, RefMut, BorrowState};
18 use marker::PhantomData;
25 use self::rt::v1::Alignment;
27 pub use self::num::radix;
28 pub use self::num::Radix;
29 pub use self::num::RadixFmt;
31 pub use self::builders::{DebugStruct, DebugTuple, DebugSet, DebugList, DebugMap};
36 #[unstable(feature = "fmt_internals", reason = "internal to format_args!")]
42 #[stable(feature = "rust1", since = "1.0.0")]
43 /// The type returned by formatter methods.
44 pub type Result = result::Result<(), Error>;
46 /// The error type which is returned from formatting a message into a stream.
48 /// This type does not support transmission of an error other than that an error
49 /// occurred. Any extra information must be arranged to be transmitted through
51 #[stable(feature = "rust1", since = "1.0.0")]
52 #[derive(Copy, Clone, Debug)]
55 /// A collection of methods that are required to format a message into a stream.
57 /// This trait is the type which this modules requires when formatting
58 /// information. This is similar to the standard library's `io::Write` trait,
59 /// but it is only intended for use in libcore.
61 /// This trait should generally not be implemented by consumers of the standard
62 /// library. The `write!` macro accepts an instance of `io::Write`, and the
63 /// `io::Write` trait is favored over implementing this trait.
64 #[stable(feature = "rust1", since = "1.0.0")]
66 /// Writes a slice of bytes into this writer, returning whether the write
69 /// This method can only succeed if the entire byte slice was successfully
70 /// written, and this method will not return until all data has been
71 /// written or an error occurs.
75 /// This function will return an instance of `Error` on error.
76 #[stable(feature = "rust1", since = "1.0.0")]
77 fn write_str(&mut self, s: &str) -> Result;
79 /// Writes a `char` into this writer, returning whether the write succeeded.
81 /// A single `char` may be encoded as more than one byte.
82 /// This method can only succeed if the entire byte sequence was successfully
83 /// written, and this method will not return until all data has been
84 /// written or an error occurs.
88 /// This function will return an instance of `Error` on error.
89 #[stable(feature = "fmt_write_char", since = "1.1.0")]
90 fn write_char(&mut self, c: char) -> Result {
91 let mut utf_8 = [0u8; 4];
92 let bytes_written = c.encode_utf8(&mut utf_8).unwrap_or(0);
93 self.write_str(unsafe { mem::transmute(&utf_8[..bytes_written]) })
96 /// Glue for usage of the `write!` macro with implementers of this trait.
98 /// This method should generally not be invoked manually, but rather through
99 /// the `write!` macro itself.
100 #[stable(feature = "rust1", since = "1.0.0")]
101 fn write_fmt(&mut self, args: Arguments) -> Result {
102 // This Adapter is needed to allow `self` (of type `&mut
103 // Self`) to be cast to a Write (below) without
104 // requiring a `Sized` bound.
105 struct Adapter<'a,T: ?Sized +'a>(&'a mut T);
107 impl<'a, T: ?Sized> Write for Adapter<'a, T>
110 fn write_str(&mut self, s: &str) -> Result {
114 fn write_fmt(&mut self, args: Arguments) -> Result {
115 self.0.write_fmt(args)
119 write(&mut Adapter(self), args)
123 /// A struct to represent both where to emit formatting strings to and how they
124 /// should be formatted. A mutable version of this is passed to all formatting
126 #[stable(feature = "rust1", since = "1.0.0")]
127 pub struct Formatter<'a> {
130 align: rt::v1::Alignment,
131 width: Option<usize>,
132 precision: Option<usize>,
134 buf: &'a mut (Write+'a),
135 curarg: slice::Iter<'a, ArgumentV1<'a>>,
136 args: &'a [ArgumentV1<'a>],
139 // NB. Argument is essentially an optimized partially applied formatting function,
140 // equivalent to `exists T.(&T, fn(&T, &mut Formatter) -> Result`.
144 /// This struct represents the generic "argument" which is taken by the Xprintf
145 /// family of functions. It contains a function to format the given value. At
146 /// compile time it is ensured that the function and the value have the correct
147 /// types, and then this struct is used to canonicalize arguments to one type.
149 #[unstable(feature = "fmt_internals", reason = "internal to format_args!")]
151 pub struct ArgumentV1<'a> {
153 formatter: fn(&Void, &mut Formatter) -> Result,
156 impl<'a> Clone for ArgumentV1<'a> {
157 fn clone(&self) -> ArgumentV1<'a> {
162 impl<'a> ArgumentV1<'a> {
164 fn show_usize(x: &usize, f: &mut Formatter) -> Result {
169 #[unstable(feature = "fmt_internals", reason = "internal to format_args!")]
170 pub fn new<'b, T>(x: &'b T,
171 f: fn(&T, &mut Formatter) -> Result) -> ArgumentV1<'b> {
174 formatter: mem::transmute(f),
175 value: mem::transmute(x)
181 #[unstable(feature = "fmt_internals", reason = "internal to format_args!")]
182 pub fn from_usize(x: &usize) -> ArgumentV1 {
183 ArgumentV1::new(x, ArgumentV1::show_usize)
186 fn as_usize(&self) -> Option<usize> {
187 if self.formatter as usize == ArgumentV1::show_usize as usize {
188 Some(unsafe { *(self.value as *const _ as *const usize) })
195 // flags available in the v1 format of format_args
196 #[derive(Copy, Clone)]
197 #[allow(dead_code)] // SignMinus isn't currently used
198 enum FlagV1 { SignPlus, SignMinus, Alternate, SignAwareZeroPad, }
200 impl<'a> Arguments<'a> {
201 /// When using the format_args!() macro, this function is used to generate the
202 /// Arguments structure.
203 #[doc(hidden)] #[inline]
204 #[unstable(feature = "fmt_internals", reason = "internal to format_args!")]
205 pub fn new_v1(pieces: &'a [&'a str],
206 args: &'a [ArgumentV1<'a>]) -> Arguments<'a> {
214 /// This function is used to specify nonstandard formatting parameters.
215 /// The `pieces` array must be at least as long as `fmt` to construct
216 /// a valid Arguments structure. Also, any `Count` within `fmt` that is
217 /// `CountIsParam` or `CountIsNextParam` has to point to an argument
218 /// created with `argumentusize`. However, failing to do so doesn't cause
219 /// unsafety, but will ignore invalid .
220 #[doc(hidden)] #[inline]
221 #[unstable(feature = "fmt_internals", reason = "internal to format_args!")]
222 pub fn new_v1_formatted(pieces: &'a [&'a str],
223 args: &'a [ArgumentV1<'a>],
224 fmt: &'a [rt::v1::Argument]) -> Arguments<'a> {
233 /// This structure represents a safely precompiled version of a format string
234 /// and its arguments. This cannot be generated at runtime because it cannot
235 /// safely be done so, so no constructors are given and the fields are private
236 /// to prevent modification.
238 /// The `format_args!` macro will safely create an instance of this structure
239 /// and pass it to a function or closure, passed as the first argument. The
240 /// macro validates the format string at compile-time so usage of the `write`
241 /// and `format` functions can be safely performed.
242 #[stable(feature = "rust1", since = "1.0.0")]
243 #[derive(Copy, Clone)]
244 pub struct Arguments<'a> {
245 // Format string pieces to print.
246 pieces: &'a [&'a str],
248 // Placeholder specs, or `None` if all specs are default (as in "{}{}").
249 fmt: Option<&'a [rt::v1::Argument]>,
251 // Dynamic arguments for interpolation, to be interleaved with string
252 // pieces. (Every argument is preceded by a string piece.)
253 args: &'a [ArgumentV1<'a>],
256 #[stable(feature = "rust1", since = "1.0.0")]
257 impl<'a> Debug for Arguments<'a> {
258 fn fmt(&self, fmt: &mut Formatter) -> Result {
259 Display::fmt(self, fmt)
263 #[stable(feature = "rust1", since = "1.0.0")]
264 impl<'a> Display for Arguments<'a> {
265 fn fmt(&self, fmt: &mut Formatter) -> Result {
266 write(fmt.buf, *self)
270 /// Format trait for the `?` character. Useful for debugging, all types
271 /// should implement this.
273 /// Generally speaking, you should just `derive` a `Debug` implementation.
277 /// Deriving an implementation:
286 /// let origin = Point { x: 0, y: 0 };
288 /// println!("The origin is: {:?}", origin);
291 /// Manually implementing:
301 /// impl fmt::Debug for Point {
302 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
303 /// write!(f, "({}, {})", self.x, self.y)
307 /// let origin = Point { x: 0, y: 0 };
309 /// println!("The origin is: {:?}", origin);
312 /// There are a number of `debug_*` methods on `Formatter` to help you with manual
313 /// implementations, such as [`debug_struct`][debug_struct].
315 /// `Debug` implementations using either `derive` or the debug builder API
316 /// on `Formatter` support pretty printing using the alternate flag: `{:#?}`.
318 /// [debug_struct]: ../std/fmt/struct.Formatter.html#method.debug_struct
319 #[stable(feature = "rust1", since = "1.0.0")]
320 #[rustc_on_unimplemented = "`{Self}` cannot be formatted using `:?`; if it is \
321 defined in your crate, add `#[derive(Debug)]` or \
322 manually implement it"]
323 #[lang = "debug_trait"]
325 /// Formats the value using the given formatter.
326 #[stable(feature = "rust1", since = "1.0.0")]
327 fn fmt(&self, &mut Formatter) -> Result;
330 /// When a value can be semantically expressed as a String, this trait may be
331 /// used. It corresponds to the default format, `{}`.
332 #[rustc_on_unimplemented = "`{Self}` cannot be formatted with the default \
333 formatter; try using `:?` instead if you are using \
335 #[stable(feature = "rust1", since = "1.0.0")]
337 /// Formats the value using the given formatter.
338 #[stable(feature = "rust1", since = "1.0.0")]
339 fn fmt(&self, &mut Formatter) -> Result;
342 /// Format trait for the `o` character
343 #[stable(feature = "rust1", since = "1.0.0")]
345 /// Formats the value using the given formatter.
346 #[stable(feature = "rust1", since = "1.0.0")]
347 fn fmt(&self, &mut Formatter) -> Result;
350 /// Format trait for the `b` character
351 #[stable(feature = "rust1", since = "1.0.0")]
353 /// Formats the value using the given formatter.
354 #[stable(feature = "rust1", since = "1.0.0")]
355 fn fmt(&self, &mut Formatter) -> Result;
358 /// Format trait for the `x` character
359 #[stable(feature = "rust1", since = "1.0.0")]
361 /// Formats the value using the given formatter.
362 #[stable(feature = "rust1", since = "1.0.0")]
363 fn fmt(&self, &mut Formatter) -> Result;
366 /// Format trait for the `X` character
367 #[stable(feature = "rust1", since = "1.0.0")]
369 /// Formats the value using the given formatter.
370 #[stable(feature = "rust1", since = "1.0.0")]
371 fn fmt(&self, &mut Formatter) -> Result;
374 /// Format trait for the `p` character
375 #[stable(feature = "rust1", since = "1.0.0")]
377 /// Formats the value using the given formatter.
378 #[stable(feature = "rust1", since = "1.0.0")]
379 fn fmt(&self, &mut Formatter) -> Result;
382 /// Format trait for the `e` character
383 #[stable(feature = "rust1", since = "1.0.0")]
385 /// Formats the value using the given formatter.
386 #[stable(feature = "rust1", since = "1.0.0")]
387 fn fmt(&self, &mut Formatter) -> Result;
390 /// Format trait for the `E` character
391 #[stable(feature = "rust1", since = "1.0.0")]
393 /// Formats the value using the given formatter.
394 #[stable(feature = "rust1", since = "1.0.0")]
395 fn fmt(&self, &mut Formatter) -> Result;
398 /// The `write` function takes an output stream, a precompiled format string,
399 /// and a list of arguments. The arguments will be formatted according to the
400 /// specified format string into the output stream provided.
404 /// * output - the buffer to write output to
405 /// * args - the precompiled arguments generated by `format_args!`
406 #[stable(feature = "rust1", since = "1.0.0")]
407 pub fn write(output: &mut Write, args: Arguments) -> Result {
408 let mut formatter = Formatter {
413 align: Alignment::Unknown,
416 curarg: args.args.iter(),
419 let mut pieces = args.pieces.iter();
423 // We can use default formatting parameters for all arguments.
424 for (arg, piece) in args.args.iter().zip(pieces.by_ref()) {
425 try!(formatter.buf.write_str(*piece));
426 try!((arg.formatter)(arg.value, &mut formatter));
430 // Every spec has a corresponding argument that is preceded by
432 for (arg, piece) in fmt.iter().zip(pieces.by_ref()) {
433 try!(formatter.buf.write_str(*piece));
434 try!(formatter.run(arg));
439 // There can be only one trailing string piece left.
440 match pieces.next() {
442 try!(formatter.buf.write_str(*piece));
450 impl<'a> Formatter<'a> {
452 // First up is the collection of functions used to execute a format string
453 // at runtime. This consumes all of the compile-time statics generated by
454 // the format! syntax extension.
455 fn run(&mut self, arg: &rt::v1::Argument) -> Result {
456 // Fill in the format parameters into the formatter
457 self.fill = arg.format.fill;
458 self.align = arg.format.align;
459 self.flags = arg.format.flags;
460 self.width = self.getcount(&arg.format.width);
461 self.precision = self.getcount(&arg.format.precision);
463 // Extract the correct argument
464 let value = match arg.position {
465 rt::v1::Position::Next => { *self.curarg.next().unwrap() }
466 rt::v1::Position::At(i) => self.args[i],
469 // Then actually do some printing
470 (value.formatter)(value.value, self)
473 fn getcount(&mut self, cnt: &rt::v1::Count) -> Option<usize> {
475 rt::v1::Count::Is(n) => Some(n),
476 rt::v1::Count::Implied => None,
477 rt::v1::Count::Param(i) => {
478 self.args[i].as_usize()
480 rt::v1::Count::NextParam => {
481 self.curarg.next().and_then(|arg| arg.as_usize())
486 // Helper methods used for padding and processing formatting arguments that
487 // all formatting traits can use.
489 /// Performs the correct padding for an integer which has already been
490 /// emitted into a str. The str should *not* contain the sign for the
491 /// integer, that will be added by this method.
495 /// * is_positive - whether the original integer was positive or not.
496 /// * prefix - if the '#' character (Alternate) is provided, this
497 /// is the prefix to put in front of the number.
498 /// * buf - the byte array that the number has been formatted into
500 /// This function will correctly account for the flags provided as well as
501 /// the minimum width. It will not take precision into account.
502 #[stable(feature = "rust1", since = "1.0.0")]
503 pub fn pad_integral(&mut self,
510 let mut width = buf.len();
514 sign = Some('-'); width += 1;
515 } else if self.flags & (1 << (FlagV1::SignPlus as u32)) != 0 {
516 sign = Some('+'); width += 1;
519 let mut prefixed = false;
520 if self.flags & (1 << (FlagV1::Alternate as u32)) != 0 {
521 prefixed = true; width += prefix.char_len();
524 // Writes the sign if it exists, and then the prefix if it was requested
525 let write_prefix = |f: &mut Formatter| {
526 if let Some(c) = sign {
528 let n = c.encode_utf8(&mut b).unwrap_or(0);
529 let b = unsafe { str::from_utf8_unchecked(&b[..n]) };
530 try!(f.buf.write_str(b));
532 if prefixed { f.buf.write_str(prefix) }
536 // The `width` field is more of a `min-width` parameter at this point.
538 // If there's no minimum length requirements then we can just
541 try!(write_prefix(self)); self.buf.write_str(buf)
543 // Check if we're over the minimum width, if so then we can also
544 // just write the bytes.
545 Some(min) if width >= min => {
546 try!(write_prefix(self)); self.buf.write_str(buf)
548 // The sign and prefix goes before the padding if the fill character
550 Some(min) if self.flags & (1 << (FlagV1::SignAwareZeroPad as u32)) != 0 => {
552 try!(write_prefix(self));
553 self.with_padding(min - width, Alignment::Right, |f| {
557 // Otherwise, the sign and prefix goes after the padding
559 self.with_padding(min - width, Alignment::Right, |f| {
560 try!(write_prefix(f)); f.buf.write_str(buf)
566 /// This function takes a string slice and emits it to the internal buffer
567 /// after applying the relevant formatting flags specified. The flags
568 /// recognized for generic strings are:
570 /// * width - the minimum width of what to emit
571 /// * fill/align - what to emit and where to emit it if the string
572 /// provided needs to be padded
573 /// * precision - the maximum length to emit, the string is truncated if it
574 /// is longer than this length
576 /// Notably this function ignored the `flag` parameters
577 #[stable(feature = "rust1", since = "1.0.0")]
578 pub fn pad(&mut self, s: &str) -> Result {
579 // Make sure there's a fast path up front
580 if self.width.is_none() && self.precision.is_none() {
581 return self.buf.write_str(s);
583 // The `precision` field can be interpreted as a `max-width` for the
584 // string being formatted
585 match self.precision {
587 // If there's a maximum width and our string is longer than
588 // that, then we must always have truncation. This is the only
589 // case where the maximum length will matter.
590 let char_len = s.char_len();
592 let nchars = ::cmp::min(max, char_len);
593 return self.buf.write_str(s.slice_chars(0, nchars));
598 // The `width` field is more of a `min-width` parameter at this point.
600 // If we're under the maximum length, and there's no minimum length
601 // requirements, then we can just emit the string
602 None => self.buf.write_str(s),
603 // If we're under the maximum width, check if we're over the minimum
604 // width, if so it's as easy as just emitting the string.
605 Some(width) if s.char_len() >= width => {
606 self.buf.write_str(s)
608 // If we're under both the maximum and the minimum width, then fill
609 // up the minimum width with the specified string + some alignment.
611 self.with_padding(width - s.char_len(), Alignment::Left, |me| {
618 /// Runs a callback, emitting the correct padding either before or
619 /// afterwards depending on whether right or left alignment is requested.
620 fn with_padding<F>(&mut self, padding: usize, default: Alignment,
622 where F: FnOnce(&mut Formatter) -> Result,
625 let align = match self.align {
626 Alignment::Unknown => default,
630 let (pre_pad, post_pad) = match align {
631 Alignment::Left => (0, padding),
632 Alignment::Right | Alignment::Unknown => (padding, 0),
633 Alignment::Center => (padding / 2, (padding + 1) / 2),
636 let mut fill = [0; 4];
637 let len = self.fill.encode_utf8(&mut fill).unwrap_or(0);
638 let fill = unsafe { str::from_utf8_unchecked(&fill[..len]) };
640 for _ in 0..pre_pad {
641 try!(self.buf.write_str(fill));
646 for _ in 0..post_pad {
647 try!(self.buf.write_str(fill));
653 /// Takes the formatted parts and applies the padding.
654 /// Assumes that the caller already has rendered the parts with required precision,
655 /// so that `self.precision` can be ignored.
656 fn pad_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
657 if let Some(mut width) = self.width {
658 // for the sign-aware zero padding, we render the sign first and
659 // behave as if we had no sign from the beginning.
660 let mut formatted = formatted.clone();
661 let mut align = self.align;
662 let old_fill = self.fill;
663 if self.flags & (1 << (FlagV1::SignAwareZeroPad as u32)) != 0 {
664 // a sign always goes first
665 let sign = unsafe { str::from_utf8_unchecked(formatted.sign) };
666 try!(self.buf.write_str(sign));
668 // remove the sign from the formatted parts
669 formatted.sign = b"";
670 width = if width < sign.len() { 0 } else { width - sign.len() };
671 align = Alignment::Right;
675 // remaining parts go through the ordinary padding process.
676 let len = formatted.len();
677 let ret = if width <= len { // no padding
678 self.write_formatted_parts(&formatted)
680 self.with_padding(width - len, align, |f| {
681 f.write_formatted_parts(&formatted)
684 self.fill = old_fill;
687 // this is the common case and we take a shortcut
688 self.write_formatted_parts(formatted)
692 fn write_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
693 fn write_bytes(buf: &mut Write, s: &[u8]) -> Result {
694 buf.write_str(unsafe { str::from_utf8_unchecked(s) })
697 if !formatted.sign.is_empty() {
698 try!(write_bytes(self.buf, formatted.sign));
700 for part in formatted.parts {
702 flt2dec::Part::Zero(mut nzeroes) => {
703 const ZEROES: &'static str = // 64 zeroes
704 "0000000000000000000000000000000000000000000000000000000000000000";
705 while nzeroes > ZEROES.len() {
706 try!(self.buf.write_str(ZEROES));
707 nzeroes -= ZEROES.len();
710 try!(self.buf.write_str(&ZEROES[..nzeroes]));
713 flt2dec::Part::Num(mut v) => {
715 let len = part.len();
716 for c in s[..len].iter_mut().rev() {
717 *c = b'0' + (v % 10) as u8;
720 try!(write_bytes(self.buf, &s[..len]));
722 flt2dec::Part::Copy(buf) => {
723 try!(write_bytes(self.buf, buf));
730 /// Writes some data to the underlying buffer contained within this
732 #[stable(feature = "rust1", since = "1.0.0")]
733 pub fn write_str(&mut self, data: &str) -> Result {
734 self.buf.write_str(data)
737 /// Writes some formatted information into this instance
738 #[stable(feature = "rust1", since = "1.0.0")]
739 pub fn write_fmt(&mut self, fmt: Arguments) -> Result {
743 /// Flags for formatting (packed version of rt::Flag)
744 #[stable(feature = "rust1", since = "1.0.0")]
745 pub fn flags(&self) -> u32 { self.flags }
747 /// Character used as 'fill' whenever there is alignment
748 #[unstable(feature = "fmt_flags", reason = "method was just created")]
749 pub fn fill(&self) -> char { self.fill }
751 /// Flag indicating what form of alignment was requested
752 #[unstable(feature = "fmt_flags", reason = "method was just created")]
753 pub fn align(&self) -> Alignment { self.align }
755 /// Optionally specified integer width that the output should be
756 #[unstable(feature = "fmt_flags", reason = "method was just created")]
757 pub fn width(&self) -> Option<usize> { self.width }
759 /// Optionally specified precision for numeric types
760 #[unstable(feature = "fmt_flags", reason = "method was just created")]
761 pub fn precision(&self) -> Option<usize> { self.precision }
763 /// Creates a `DebugStruct` builder designed to assist with creation of
764 /// `fmt::Debug` implementations for structs.
776 /// impl fmt::Debug for Foo {
777 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
778 /// fmt.debug_struct("Foo")
779 /// .field("bar", &self.bar)
780 /// .field("baz", &self.baz)
785 /// // prints "Foo { bar: 10, baz: "Hello World" }"
786 /// println!("{:?}", Foo { bar: 10, baz: "Hello World".to_string() });
788 #[stable(feature = "debug_builders", since = "1.2.0")]
790 pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
791 builders::debug_struct_new(self, name)
794 /// Creates a `DebugTuple` builder designed to assist with creation of
795 /// `fmt::Debug` implementations for tuple structs.
802 /// struct Foo(i32, String);
804 /// impl fmt::Debug for Foo {
805 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
806 /// fmt.debug_tuple("Foo")
813 /// // prints "Foo(10, "Hello World")"
814 /// println!("{:?}", Foo(10, "Hello World".to_string()));
816 #[stable(feature = "debug_builders", since = "1.2.0")]
818 pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
819 builders::debug_tuple_new(self, name)
822 /// Creates a `DebugList` builder designed to assist with creation of
823 /// `fmt::Debug` implementations for list-like structures.
830 /// struct Foo(Vec<i32>);
832 /// impl fmt::Debug for Foo {
833 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
834 /// fmt.debug_list().entries(self.0.iter()).finish()
838 /// // prints "[10, 11]"
839 /// println!("{:?}", Foo(vec![10, 11]));
841 #[stable(feature = "debug_builders", since = "1.2.0")]
843 pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
844 builders::debug_list_new(self)
847 /// Creates a `DebugSet` builder designed to assist with creation of
848 /// `fmt::Debug` implementations for set-like structures.
855 /// struct Foo(Vec<i32>);
857 /// impl fmt::Debug for Foo {
858 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
859 /// fmt.debug_set().entries(self.0.iter()).finish()
863 /// // prints "{10, 11}"
864 /// println!("{:?}", Foo(vec![10, 11]));
866 #[stable(feature = "debug_builders", since = "1.2.0")]
868 pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
869 builders::debug_set_new(self)
872 /// Creates a `DebugMap` builder designed to assist with creation of
873 /// `fmt::Debug` implementations for map-like structures.
880 /// struct Foo(Vec<(String, i32)>);
882 /// impl fmt::Debug for Foo {
883 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
884 /// fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
888 /// // prints "{"A": 10, "B": 11}"
889 /// println!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)]));
891 #[stable(feature = "debug_builders", since = "1.2.0")]
893 pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
894 builders::debug_map_new(self)
898 #[stable(since = "1.2.0", feature = "formatter_write")]
899 impl<'a> Write for Formatter<'a> {
900 fn write_str(&mut self, s: &str) -> Result {
901 self.buf.write_str(s)
904 fn write_char(&mut self, c: char) -> Result {
905 self.buf.write_char(c)
908 fn write_fmt(&mut self, args: Arguments) -> Result {
909 write(self.buf, args)
913 #[stable(feature = "rust1", since = "1.0.0")]
914 impl Display for Error {
915 fn fmt(&self, f: &mut Formatter) -> Result {
916 Display::fmt("an error occurred when formatting an argument", f)
920 // Implementations of the core formatting traits
922 macro_rules! fmt_refs {
923 ($($tr:ident),*) => {
925 #[stable(feature = "rust1", since = "1.0.0")]
926 impl<'a, T: ?Sized + $tr> $tr for &'a T {
927 fn fmt(&self, f: &mut Formatter) -> Result { $tr::fmt(&**self, f) }
929 #[stable(feature = "rust1", since = "1.0.0")]
930 impl<'a, T: ?Sized + $tr> $tr for &'a mut T {
931 fn fmt(&self, f: &mut Formatter) -> Result { $tr::fmt(&**self, f) }
937 fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
939 #[stable(feature = "rust1", since = "1.0.0")]
940 impl Debug for bool {
941 fn fmt(&self, f: &mut Formatter) -> Result {
942 Display::fmt(self, f)
946 #[stable(feature = "rust1", since = "1.0.0")]
947 impl Display for bool {
948 fn fmt(&self, f: &mut Formatter) -> Result {
949 Display::fmt(if *self { "true" } else { "false" }, f)
953 #[stable(feature = "rust1", since = "1.0.0")]
955 fn fmt(&self, f: &mut Formatter) -> Result {
956 try!(write!(f, "\""));
957 for c in self.chars().flat_map(|c| c.escape_default()) {
958 try!(write!(f, "{}", c));
964 #[stable(feature = "rust1", since = "1.0.0")]
965 impl Display for str {
966 fn fmt(&self, f: &mut Formatter) -> Result {
971 #[stable(feature = "rust1", since = "1.0.0")]
972 impl Debug for char {
973 fn fmt(&self, f: &mut Formatter) -> Result {
975 try!(write!(f, "'"));
976 for c in self.escape_default() {
977 try!(write!(f, "{}", c));
983 #[stable(feature = "rust1", since = "1.0.0")]
984 impl Display for char {
985 fn fmt(&self, f: &mut Formatter) -> Result {
986 if f.width.is_none() && f.precision.is_none() {
989 let mut utf8 = [0; 4];
990 let amt = self.encode_utf8(&mut utf8).unwrap_or(0);
991 let s: &str = unsafe { mem::transmute(&utf8[..amt]) };
997 #[stable(feature = "rust1", since = "1.0.0")]
998 impl<T> Pointer for *const T {
999 fn fmt(&self, f: &mut Formatter) -> Result {
1000 let old_width = f.width;
1001 let old_flags = f.flags;
1003 // The alternate flag is already treated by LowerHex as being special-
1004 // it denotes whether to prefix with 0x. We use it to work out whether
1005 // or not to zero extend, and then unconditionally set it to get the
1007 if f.flags & 1 << (FlagV1::Alternate as u32) > 0 {
1008 f.flags |= 1 << (FlagV1::SignAwareZeroPad as u32);
1010 if let None = f.width {
1011 // The formats need two extra bytes, for the 0x
1012 if cfg!(target_pointer_width = "32") {
1019 f.flags |= 1 << (FlagV1::Alternate as u32);
1021 let ret = LowerHex::fmt(&(*self as usize), f);
1023 f.width = old_width;
1024 f.flags = old_flags;
1030 #[stable(feature = "rust1", since = "1.0.0")]
1031 impl<T> Pointer for *mut T {
1032 fn fmt(&self, f: &mut Formatter) -> Result {
1033 // FIXME(#23542) Replace with type ascription.
1034 #![allow(trivial_casts)]
1035 Pointer::fmt(&(*self as *const T), f)
1039 #[stable(feature = "rust1", since = "1.0.0")]
1040 impl<'a, T> Pointer for &'a T {
1041 fn fmt(&self, f: &mut Formatter) -> Result {
1042 // FIXME(#23542) Replace with type ascription.
1043 #![allow(trivial_casts)]
1044 Pointer::fmt(&(*self as *const T), f)
1048 #[stable(feature = "rust1", since = "1.0.0")]
1049 impl<'a, T> Pointer for &'a mut T {
1050 fn fmt(&self, f: &mut Formatter) -> Result {
1051 // FIXME(#23542) Replace with type ascription.
1052 #![allow(trivial_casts)]
1053 Pointer::fmt(&(&**self as *const T), f)
1057 // Common code of floating point Debug and Display.
1058 fn float_to_decimal_common<T>(fmt: &mut Formatter, num: &T, negative_zero: bool) -> Result
1059 where T: flt2dec::DecodableFloat
1061 let force_sign = fmt.flags & (1 << (FlagV1::SignPlus as u32)) != 0;
1062 let sign = match (force_sign, negative_zero) {
1063 (false, false) => flt2dec::Sign::Minus,
1064 (false, true) => flt2dec::Sign::MinusRaw,
1065 (true, false) => flt2dec::Sign::MinusPlus,
1066 (true, true) => flt2dec::Sign::MinusPlusRaw,
1069 let mut buf = [0; 1024]; // enough for f32 and f64
1070 let mut parts = [flt2dec::Part::Zero(0); 16];
1071 let formatted = if let Some(precision) = fmt.precision {
1072 flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact, *num, sign,
1073 precision, false, &mut buf, &mut parts)
1075 flt2dec::to_shortest_str(flt2dec::strategy::grisu::format_shortest, *num, sign,
1076 0, false, &mut buf, &mut parts)
1078 fmt.pad_formatted_parts(&formatted)
1081 // Common code of floating point LowerExp and UpperExp.
1082 fn float_to_exponential_common<T>(fmt: &mut Formatter, num: &T, upper: bool) -> Result
1083 where T: flt2dec::DecodableFloat
1085 let force_sign = fmt.flags & (1 << (FlagV1::SignPlus as u32)) != 0;
1086 let sign = match force_sign {
1087 false => flt2dec::Sign::Minus,
1088 true => flt2dec::Sign::MinusPlus,
1091 let mut buf = [0; 1024]; // enough for f32 and f64
1092 let mut parts = [flt2dec::Part::Zero(0); 16];
1093 let formatted = if let Some(precision) = fmt.precision {
1094 // 1 integral digit + `precision` fractional digits = `precision + 1` total digits
1095 flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact, *num, sign,
1096 precision + 1, upper, &mut buf, &mut parts)
1098 flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest, *num, sign,
1099 (0, 0), upper, &mut buf, &mut parts)
1101 fmt.pad_formatted_parts(&formatted)
1104 macro_rules! floating { ($ty:ident) => {
1106 #[stable(feature = "rust1", since = "1.0.0")]
1107 impl Debug for $ty {
1108 fn fmt(&self, fmt: &mut Formatter) -> Result {
1109 float_to_decimal_common(fmt, self, true)
1113 #[stable(feature = "rust1", since = "1.0.0")]
1114 impl Display for $ty {
1115 fn fmt(&self, fmt: &mut Formatter) -> Result {
1116 float_to_decimal_common(fmt, self, false)
1120 #[stable(feature = "rust1", since = "1.0.0")]
1121 impl LowerExp for $ty {
1122 fn fmt(&self, fmt: &mut Formatter) -> Result {
1123 float_to_exponential_common(fmt, self, false)
1127 #[stable(feature = "rust1", since = "1.0.0")]
1128 impl UpperExp for $ty {
1129 fn fmt(&self, fmt: &mut Formatter) -> Result {
1130 float_to_exponential_common(fmt, self, true)
1137 // Implementation of Display/Debug for various core types
1139 #[stable(feature = "rust1", since = "1.0.0")]
1140 impl<T> Debug for *const T {
1141 fn fmt(&self, f: &mut Formatter) -> Result { Pointer::fmt(self, f) }
1143 #[stable(feature = "rust1", since = "1.0.0")]
1144 impl<T> Debug for *mut T {
1145 fn fmt(&self, f: &mut Formatter) -> Result { Pointer::fmt(self, f) }
1149 ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
1152 macro_rules! tuple {
1154 ( $($name:ident,)+ ) => (
1155 #[stable(feature = "rust1", since = "1.0.0")]
1156 impl<$($name:Debug),*> Debug for ($($name,)*) {
1157 #[allow(non_snake_case, unused_assignments)]
1158 fn fmt(&self, f: &mut Formatter) -> Result {
1159 try!(write!(f, "("));
1160 let ($(ref $name,)*) = *self;
1164 try!(write!(f, ", "));
1166 try!(write!(f, "{:?}", *$name));
1170 try!(write!(f, ","));
1175 peel! { $($name,)* }
1179 tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }
1181 #[stable(feature = "rust1", since = "1.0.0")]
1182 impl<T: Debug> Debug for [T] {
1183 fn fmt(&self, f: &mut Formatter) -> Result {
1184 f.debug_list().entries(self.iter()).finish()
1188 #[stable(feature = "rust1", since = "1.0.0")]
1190 fn fmt(&self, f: &mut Formatter) -> Result {
1194 impl<T> Debug for PhantomData<T> {
1195 fn fmt(&self, f: &mut Formatter) -> Result {
1196 f.pad("PhantomData")
1200 #[stable(feature = "rust1", since = "1.0.0")]
1201 impl<T: Copy + Debug> Debug for Cell<T> {
1202 fn fmt(&self, f: &mut Formatter) -> Result {
1203 write!(f, "Cell {{ value: {:?} }}", self.get())
1207 #[stable(feature = "rust1", since = "1.0.0")]
1208 impl<T: ?Sized + Debug> Debug for RefCell<T> {
1209 fn fmt(&self, f: &mut Formatter) -> Result {
1210 match self.borrow_state() {
1211 BorrowState::Unused | BorrowState::Reading => {
1212 write!(f, "RefCell {{ value: {:?} }}", self.borrow())
1214 BorrowState::Writing => write!(f, "RefCell {{ <borrowed> }}"),
1219 #[stable(feature = "rust1", since = "1.0.0")]
1220 impl<'b, T: ?Sized + Debug> Debug for Ref<'b, T> {
1221 fn fmt(&self, f: &mut Formatter) -> Result {
1222 Debug::fmt(&**self, f)
1226 #[stable(feature = "rust1", since = "1.0.0")]
1227 impl<'b, T: ?Sized + Debug> Debug for RefMut<'b, T> {
1228 fn fmt(&self, f: &mut Formatter) -> Result {
1229 Debug::fmt(&*(self.deref()), f)
1233 // If you expected tests to be here, look instead at the run-pass/ifmt.rs test,
1234 // it's a lot easier than creating all of the rt::Piece structures here.