Constify methods that transmute

* AsciiChar::from_ascii_unchecked()
* AsciiChar::as_printable_char()

Author: tormol

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [1.44.1, stable, beta, nightly]
+        rust: [1.56.1, stable, beta, nightly]
     steps:
       - uses: actions/checkout@v2
       - uses: hecrj/setup-rust-action@v1

README.md

@@ -35,12 +35,12 @@ ascii = { version = "1.0", default-features = false, features = ["alloc"] }
 
 ## Minimum supported Rust version
 
-The minimum Rust version for 1.1.\* releases is 1.44.0.
+The minimum Rust version for 1.1.\* releases is 1.56.0.
 Later 1.y.0 releases might require newer Rust versions, but the three most
 recent stable releases at the time of publishing will always be supported.  
-For example this means that if the current stable Rust version is 1.50 when
+For example this means that if the current stable Rust version is 1.70 when
 ascii 1.2.0 is released, then ascii 1.2.\* will not require a newer
-Rust version than 1.48.
+Rust version than 1.68.
 
 ## History
 

src/ascii_char.rs

@@ -375,9 +375,9 @@ impl AsciiChar {
     /// and `Some(AsciiChar::from_ascii_unchecked(128))` might be `None`.
     #[inline]
     #[must_use]
-    pub unsafe fn from_ascii_unchecked(ch: u8) -> Self {
+    pub const unsafe fn from_ascii_unchecked(ch: u8) -> Self {
         // SAFETY: Caller guarantees `ch` is within bounds of ascii.
-        unsafe { ch.to_ascii_char_unchecked() }
+        unsafe { mem::transmute(ch) }
     }
 
     /// Converts an ASCII character into a `u8`.
@@ -659,14 +659,15 @@ impl AsciiChar {
     /// assert_eq!(AsciiChar::new('p').as_printable_char(), 'p');
     /// ```
     #[must_use]
-    pub fn as_printable_char(self) -> char {
+    pub const fn as_printable_char(self) -> char {
+        #![allow(clippy::transmute_int_to_char)] // from_utf32_unchecked() is not const fn yet.
         match self as u8 {
             // Non printable characters
             // SAFETY: From codepoint 0x2400 ('␀') to 0x241f (`␟`), there are characters representing
             //         the unprintable characters from 0x0 to 0x1f, ordered correctly.
             //         As `b` is guaranteed to be within 0x0 to 0x1f, the conversion represents a
             //         valid character.
-            b @ 0x0..=0x1f => unsafe { char::from_u32_unchecked(u32::from('␀') + u32::from(b)) },
+            b @ 0x0..=0x1f => unsafe { mem::transmute('␀' as u32 + b as u32) },
 
             // 0x7f (delete) has it's own character at codepoint 0x2420, not 0x247f, so it is special
             // cased to return it's character

src/lib.rs

@@ -15,12 +15,12 @@
 //!
 //! # Minimum supported Rust version
 //!
-//! The minimum Rust version for 1.1.\* releases is 1.44.0.
+//! The minimum Rust version for 1.1.\* releases is 1.56.0.
 //! Later 1.y.0 releases might require newer Rust versions, but the three most
 //! recent stable releases at the time of publishing will always be supported.  
-//! For example this means that if the current stable Rust version is 1.50 when
+//! For example this means that if the current stable Rust version is 1.70 when
 //! ascii 1.2.0 is released, then ascii 1.2.* will not require a newer
-//! Rust version than 1.48.
+//! Rust version than 1.68.
 //!
 //! # History
 //!