# Add an easier way to append \`T: Display\` to \`String\` to stdlib? **URL:** \ **Category:** libs\ **Created:** [July 20, 2019, 1:25pm UTC](https://internals.rust-lang.org/t/add-an-easier-way-to-append-t-display-to-string-to-stdlib/10607 "2019-07-20T13:25:45Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![Boomshroom](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/boomshroom/32/5932_2.png) [@Boomshroom](https://internals.rust-lang.org/u/Boomshroom)\ **Post date:** [July 26, 2019, 8:56pm UTC](https://internals.rust-lang.org/t/add-an-easier-way-to-append-t-display-to-string-to-stdlib/10607/21 "2019-07-26T20:56:41Z")
> A collection of methods that are required to format a message into a stream. > > This trait is the type which this modules requires when formatting information. **This is similar to the standard library's io::Write trait, but it is only intended for use in libcore.** > > This trait should generally not be implemented by consumers of the standard library. The write! macro accepts an instance of io::Write, and **the io::Write trait is favored over implementing this trait.** It seems the main reason `fmt::Write` exists at all is just because `core::io` stubbornly refuses to exist. Why doesn't it again? Aside from adding `io` to `core`, one possible solution to the `Write` ambiguity would be to have `Error` be an associated type to `fmt::Result`. For `String`, `Error` would be `!`, and `io::Write` could be aliased to `fmt::Write`. I would absolutely love to be able to use `write!()` without importing. Heck, would it possible for `core::write!()` itself to `use core::fmt::Write;` and `std::write!()` to `use std::io::Write;`? If `core::io` was a thing, then `fmt::Write` could just be deleted entirely, or simply deprecated for backwards compatibility. ---
**Author:** ![ExpHP](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/exphp/32/6208_2.png) [@ExpHP](https://internals.rust-lang.org/u/ExpHP)\ **Post date:** [July 26, 2019, 9:03pm UTC](https://internals.rust-lang.org/t/add-an-easier-way-to-append-t-display-to-string-to-stdlib/10607/22 "2019-07-26T21:03:33Z")
> [@Boomshroom](#): > > If `core::io` was a thing, then `fmt::Write` could just be deleted entirely, or simply deprecated for backwards compatibility. `io::Write` can't be implemented for `String` because it can be used to write arbitrary bytes. ---
**Author:** ![MikailBag](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/mikailbag/32/5376_2.png) [@MikailBag](https://internals.rust-lang.org/u/MikailBag)\ **Post date:** [July 29, 2019, 4:51pm UTC](https://internals.rust-lang.org/t/add-an-easier-way-to-append-t-display-to-string-to-stdlib/10607/23 "2019-07-29T16:51:51Z")
io::Write String can return "invalid data" error if buf given is not utf8 ---
**Author:** ![ExpHP](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/exphp/32/6208_2.png) [@ExpHP](https://internals.rust-lang.org/u/ExpHP)\ **Post date:** [July 29, 2019, 4:58pm UTC](https://internals.rust-lang.org/t/add-an-easier-way-to-append-t-display-to-string-to-stdlib/10607/24 "2019-07-29T16:58:59Z")
But what if somebody calls `write_all` with input that ends in the middle of a character? ---
**Author:** ![MikailBag](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/mikailbag/32/5376_2.png) [@MikailBag](https://internals.rust-lang.org/u/MikailBag)\ **Post date:** [July 29, 2019, 5:20pm UTC](https://internals.rust-lang.org/t/add-an-easier-way-to-append-t-display-to-string-to-stdlib/10607/25 "2019-07-29T17:20:04Z")
I think error should be returned. This behavior would be enough for format! needs, to my mind. ---
**Author:** ![ExpHP](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/exphp/32/6208_2.png) [@ExpHP](https://internals.rust-lang.org/u/ExpHP)\ **Post date:** [July 29, 2019, 6:32pm UTC](https://internals.rust-lang.org/t/add-an-easier-way-to-append-t-display-to-string-to-stdlib/10607/26 "2019-07-29T18:32:59Z")
But splitting up a write into multiple calls should not change the results. Otherwise, something like `BufWriter` could not exist. ---
**Author:** ![system](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/system/32/14092_2.png) [@system](https://internals.rust-lang.org/u/system)\ **Post date:** [October 27, 2019, 6:48pm UTC](https://internals.rust-lang.org/t/add-an-easier-way-to-append-t-display-to-string-to-stdlib/10607/27 "2019-10-27T18:48:23Z")
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