Add hexadecimal formatting of integers with fmt::Debug #48978
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This can be used for integers within a larger types which implements Debug
(possibly through derive) but not fmt::UpperHex or fmt::LowerHex.
```rust
assert!(format!("{:02x?}", b"Foo\0") == "[46, 6f, 6f, 00]");
assert!(format!("{:02X?}", b"Foo\0") == "[46, 6F, 6F, 00]");
```
RFC: rust-lang/rfcs#2226
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Ping from triage, @KodrAus ! |
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Thanks @SimonSapin! So, as I understand it, we've got special DebugLowerHex, and DebugUpperHex variants because hex is a nice representation for bit-packed data, so we don't need to combine other formatting flags with ?.
At first I thought it was a little unfortunate that we can't treat ? like a flag that could be combined with others arbitrarily, but looking at the changes that need to be made to the Debug impls on numbers this doesn't seem like such a problem.
So all that's to say this looks good to me!
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@bors r+ |
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📌 Commit 4897935 has been approved by |
bors
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And yes, in the current implementation the fact that |
Add hexadecimal formatting of integers with fmt::Debug
This can be used for integers within a larger types which implements Debug (possibly through derive) but not fmt::UpperHex or fmt::LowerHex.
```rust
assert!(format!("{:02x?}", b"Foo\0") == "[46, 6f, 6f, 00]");
assert!(format!("{:02X?}", b"Foo\0") == "[46, 6F, 6F, 00]");
```
RFC: rust-lang/rfcs#2226
The new formatting string syntax (`x?` and `X?`) is insta-stable in this PR because I don’t know how to change a built-in proc macro’s behavior based of a feature gate. I can look into adding that, but I also strongly suspect that keeping this feature unstable for a time period would not be useful as possibly no-one would use it during that time.
This PR does not add the new (public) `fmt::Formatter` proposed in the API because:
* There was some skepticism on response to this part of the RFC
* It is not possible to implement as-is without larger changes to `fmt`, because `Formatter` at the moment has no easy way to tell apart for example `Octal` from `Binary`: it only has a function pointer for the relevant `fmt()` method.
If some integer-like type outside of `std` want to implement this behavior, another RFC will likely need to propose a different public API for `Formatter`.
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☀️ Test successful - status-appveyor, status-travis |
SimonSapin
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I’m unsure if this is release-notes-worthy, tagging to let someone else decide. |
This can be used for integers within a larger types which implements Debug (possibly through derive) but not fmt::UpperHex or fmt::LowerHex.
RFC: rust-lang/rfcs#2226
The new formatting string syntax (
x?andX?) is insta-stable in this PR because I don’t know how to change a built-in proc macro’s behavior based of a feature gate. I can look into adding that, but I also strongly suspect that keeping this feature unstable for a time period would not be useful as possibly no-one would use it during that time.This PR does not add the new (public)
fmt::Formatterproposed in the API because:fmt, becauseFormatterat the moment has no easy way to tell apart for exampleOctalfromBinary: it only has a function pointer for the relevantfmt()method.If some integer-like type outside of
stdwant to implement this behavior, another RFC will likely need to propose a different public API forFormatter.