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Tracking issue for const char conversions #89259

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est31 opened this issue Sep 25, 2021 · 7 comments
Open

Tracking issue for const char conversions #89259

est31 opened this issue Sep 25, 2021 · 7 comments
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C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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@est31
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est31 commented Sep 25, 2021 •
edited

This is a tracking issue for const char conversions. List of functions belonging to !#[feature(const_char_from_u32_unchecked)]:

impl char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}

// Available through core::char and std::char
mod char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}

List of functions belonging to stable #![feature(const_char_convert)]:

impl char {
    pub const fn from_u32(self, i: u32) -> Option<char>;
    pub const fn from_digit(self, num: u32, radix: u32) -> Option<char>;
    pub const fn to_digit(self, radix: u32) -> Option<u32>;
}

// Available through core::char and std::char
mod char {
    pub const fn from_u32(i: u32) -> Option<char>;
    pub const fn from_digit(num: u32, radix: u32) -> Option<char>;
}

Steps:

Stabilization is probably blocked by const panicing. Edit: const panic is stable now!

Stabilization is blocked by Option::unwrap const stability, which is blocked by #73255.
@est31 est31 added C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. labels Sep 25, 2021
@est31 est31 mentioned this issue Sep 25, 2021
Merged
@leonardo-m
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We could keep a percentage counter somewhere that tells how much of stdlib is areweconstyet :)

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Nov 18, 2021
@matthiaskrgr
Rollup merge of rust-lang#89258 - est31:const_char_convert, r=oli-obk
0e39dca 
Make char conversion functions unstably const

The char conversion functions like `char::from_u32` do trivial computations and can easily be converted into const fns. Only smaller tricks are needed to avoid non-const standard library functions like `Result::ok` or `bool::then_some`.

Tracking issue: rust-lang#89259
JohnTitor added a commit to JohnTitor/rust that referenced this issue Nov 19, 2021
@JohnTitor
Rollup merge of rust-lang#89258 - est31:const_char_convert, r=oli-obk
7432588 
Make char conversion functions unstably const

The char conversion functions like `char::from_u32` do trivial computations and can easily be converted into const fns. Only smaller tricks are needed to avoid non-const standard library functions like `Result::ok` or `bool::then_some`.

Tracking issue: rust-lang#89259
@Nugine
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Nugine commented Sep 29, 2022

Hi! Is there any plan of stabilization?

@est31 est31 mentioned this issue Sep 29, 2022
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@est31
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est31 commented Sep 29, 2022

@Nugine I've made a stabilization PR, let's see where this goes: #102470

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Nov 14, 2022
@matthiaskrgr
Rollup merge of rust-lang#102470 - est31:stabilize_const_char_convert…
ab87c4c 
…, r=joshtriplett

Stabilize const char convert

Split out `const_char_from_u32_unchecked` from `const_char_convert` and stabilize the rest, i.e. stabilize the following functions:

```Rust
impl char {
    pub const fn from_u32(self, i: u32) -> Option<char>;
    pub const fn from_digit(self, num: u32, radix: u32) -> Option<char>;
    pub const fn to_digit(self, radix: u32) -> Option<u32>;
}

// Available through core::char and std::char
mod char {
    pub const fn from_u32(i: u32) -> Option<char>;
    pub const fn from_digit(num: u32, radix: u32) -> Option<char>;
}
```

And put the following under the `from_u32_unchecked` const stability gate as it needs `Option::unwrap` which isn't const-stable (yet):

```Rust
impl char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}

// Available through core::char and std::char
mod char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}
```

cc the tracking issue rust-lang#89259 (which I'd like to keep open for `const_char_from_u32_unchecked`).
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Nov 14, 2022
@matthiaskrgr
Rollup merge of rust-lang#102470 - est31:stabilize_const_char_convert…
749ecab 
…, r=joshtriplett

Stabilize const char convert

Split out `const_char_from_u32_unchecked` from `const_char_convert` and stabilize the rest, i.e. stabilize the following functions:

```Rust
impl char {
    pub const fn from_u32(self, i: u32) -> Option<char>;
    pub const fn from_digit(self, num: u32, radix: u32) -> Option<char>;
    pub const fn to_digit(self, radix: u32) -> Option<u32>;
}

// Available through core::char and std::char
mod char {
    pub const fn from_u32(i: u32) -> Option<char>;
    pub const fn from_digit(num: u32, radix: u32) -> Option<char>;
}
```

And put the following under the `from_u32_unchecked` const stability gate as it needs `Option::unwrap` which isn't const-stable (yet):

```Rust
impl char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}

// Available through core::char and std::char
mod char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}
```

cc the tracking issue rust-lang#89259 (which I'd like to keep open for `const_char_from_u32_unchecked`).
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Nov 14, 2022
@matthiaskrgr
Rollup merge of rust-lang#102470 - est31:stabilize_const_char_convert…
8c77da8 
…, r=joshtriplett

Stabilize const char convert

Split out `const_char_from_u32_unchecked` from `const_char_convert` and stabilize the rest, i.e. stabilize the following functions:

```Rust
impl char {
    pub const fn from_u32(self, i: u32) -> Option<char>;
    pub const fn from_digit(self, num: u32, radix: u32) -> Option<char>;
    pub const fn to_digit(self, radix: u32) -> Option<u32>;
}

// Available through core::char and std::char
mod char {
    pub const fn from_u32(i: u32) -> Option<char>;
    pub const fn from_digit(num: u32, radix: u32) -> Option<char>;
}
```

And put the following under the `from_u32_unchecked` const stability gate as it needs `Option::unwrap` which isn't const-stable (yet):

```Rust
impl char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}

// Available through core::char and std::char
mod char {
    pub const unsafe fn from_u32_unchecked(i: u32) -> char;
}
```

cc the tracking issue rust-lang#89259 (which I'd like to keep open for `const_char_from_u32_unchecked`).
@ChrisDenton
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Stabilization is blocked by #67441 const stability, which is blocked by #73255.

Could we not manually write out a match statement instead of using unwrap?

@est31
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est31 commented Dec 15, 2023

I think the idea was that there should be no extra hacks done just to get things compatible with const fn, but I don't remember it fully any more.

@ChrisDenton
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I've opened #118979 to see what T-libs thinks about it.

@ChrisDenton ChrisDenton mentioned this issue Dec 15, 2023
Merged
@ChrisDenton
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#118979 is now merged so I think there's no blocker for from_u32_unchecked being stabilized as const.

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