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Make char and u8 methods const #79549

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Make char and u8 methods const #79549

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e92a788
Make char methods const
YenForYang Nov 30, 2020
5ac8379
u8 methods made const
YenForYang Nov 30, 2020
0091322
Update methods.rs
YenForYang Nov 30, 2020
a7de9c1
Update mod.rs
YenForYang Nov 30, 2020
0a4416c
Update methods.rs
YenForYang Nov 30, 2020
9060936
Fix `since` in rustc_const_stable to next stable
YenForYang Dec 1, 2020
4337b2a
Fix `since` in rustc_const_stable to next stable
YenForYang Dec 1, 2020
b5cf6ad
Update methods.rs
YenForYang Dec 1, 2020
8b303a6
Update mod.rs
YenForYang Dec 1, 2020
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23 changes: 15 additions & 8 deletions library/core/src/char/methods.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -390,8 +390,9 @@ impl char {
/// assert_eq!('❤'.escape_unicode().to_string(), "\\u{2764}");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_char_escape_unicode", since = "1.49.0")]
#[inline]
pub fn escape_unicode(self) -> EscapeUnicode {
pub const fn escape_unicode(self) -> EscapeUnicode {
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When would this ever be called in a const context given that it returns an iterator?

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Good point, I didn't really consider the practicality for making it const. I'm not sure about the downsides of making it callable in const context, but I'm totally fine with removing it. It'll probably be a good while before const iterators happen anyway.

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I'm not sure about the downsides of making it callable in const context, but I'm totally fine with removing it.

Yeah, please remove the iterator functions.

let c = self as u32;

// or-ing 1 ensures that for c==0 the code computes that one
Expand Down Expand Up @@ -517,8 +518,9 @@ impl char {
/// assert_eq!('"'.escape_default().to_string(), "\\\"");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_char_escape_default", since = "1.49.0")]
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#[inline]
pub fn escape_default(self) -> EscapeDefault {
pub const fn escape_default(self) -> EscapeDefault {
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@oli-obk oli-obk Dec 2, 2020 •
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same here. I think we should not make functions const fn for now unless their result can actually be used for anything during const eval or there's a good reason to have a constant version of it. Unfortunately we are not yet at the "because we can" stage of making things const

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This concern seems to still be outstanding.

let init_state = match self {
'\t' => EscapeDefaultState::Backslash('t'),
'\r' => EscapeDefaultState::Backslash('r'),
Expand Down Expand Up @@ -576,8 +578,9 @@ impl char {
/// assert_eq!(len, tokyo.len());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_char_len_utf", since = "1.49.0")]
#[inline]
pub fn len_utf8(self) -> usize {
pub const fn len_utf8(self) -> usize {
len_utf8(self as u32)
}

Expand All @@ -601,8 +604,9 @@ impl char {
/// assert_eq!(len, 2);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_char_len_utf", since = "1.49.0")]
#[inline]
pub fn len_utf16(self) -> usize {
pub const fn len_utf16(self) -> usize {
let ch = self as u32;
if (ch & 0xFFFF) == ch { 1 } else { 2 }
}
Expand Down Expand Up @@ -1093,8 +1097,9 @@ impl char {
/// [`make_ascii_uppercase`]: #method.make_ascii_uppercase
/// [`to_uppercase`]: #method.to_uppercase
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.49.0")]
#[inline]
pub fn to_ascii_uppercase(&self) -> char {
pub const fn to_ascii_uppercase(&self) -> char {
if self.is_ascii() { (*self as u8).to_ascii_uppercase() as char } else { *self }
}

Expand All @@ -1121,8 +1126,9 @@ impl char {
/// [`make_ascii_lowercase`]: #method.make_ascii_lowercase
/// [`to_lowercase`]: #method.to_lowercase
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.49.0")]
#[inline]
pub fn to_ascii_lowercase(&self) -> char {
pub const fn to_ascii_lowercase(&self) -> char {
if self.is_ascii() { (*self as u8).to_ascii_lowercase() as char } else { *self }
}

Expand All @@ -1142,8 +1148,9 @@ impl char {
/// assert!(!upper_a.eq_ignore_ascii_case(&lower_z));
/// ```
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.49.0")]
#[inline]
pub fn eq_ignore_ascii_case(&self, other: &char) -> bool {
pub const fn eq_ignore_ascii_case(&self, other: &char) -> bool {
self.to_ascii_lowercase() == other.to_ascii_lowercase()
}

Expand Down Expand Up @@ -1560,7 +1567,7 @@ impl char {
}

#[inline]
fn len_utf8(code: u32) -> usize {
const fn len_utf8(code: u32) -> usize {
if code < MAX_ONE_B {
1
} else if code < MAX_TWO_B {
Expand Down
9 changes: 6 additions & 3 deletions library/core/src/num/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -199,8 +199,9 @@ impl u8 {
///
/// [`make_ascii_uppercase`]: #method.make_ascii_uppercase
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.49.0")]
#[inline]
pub fn to_ascii_uppercase(&self) -> u8 {
pub const fn to_ascii_uppercase(&self) -> u8 {
// Unset the fifth bit if this is a lowercase letter
*self & !((self.is_ascii_lowercase() as u8) << 5)
}
Expand All @@ -222,8 +223,9 @@ impl u8 {
///
/// [`make_ascii_lowercase`]: #method.make_ascii_lowercase
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.49.0")]
#[inline]
pub fn to_ascii_lowercase(&self) -> u8 {
pub const fn to_ascii_lowercase(&self) -> u8 {
// Set the fifth bit if this is an uppercase letter
*self | ((self.is_ascii_uppercase() as u8) << 5)
}
Expand All @@ -241,8 +243,9 @@ impl u8 {
/// assert!(lowercase_a.eq_ignore_ascii_case(&uppercase_a));
/// ```
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
#[rustc_const_stable(feature = "const_ascii_methods_on_intrinsics", since = "1.49.0")]
#[inline]
pub fn eq_ignore_ascii_case(&self, other: &u8) -> bool {
pub const fn eq_ignore_ascii_case(&self, other: &u8) -> bool {
self.to_ascii_lowercase() == other.to_ascii_lowercase()
}

Expand Down