Add const functions to generate a &'static str from Encoding

Will be used at some point when generic constants are available, see #70

objc2-encode/src/lib.rs

@@ -107,5 +107,9 @@ mod encode;
 mod encoding;
 mod parse;
 
+// Will be used at some point when generic constants are available
+#[allow(dead_code)]
+mod static_str;
+
 pub use self::encode::{Encode, EncodeArguments, RefEncode};
 pub use self::encoding::Encoding;

objc2-encode/src/static_str.rs

@@ -0,0 +1,264 @@
+use super::Encoding;
+
+pub(crate) const fn static_int_str_len(mut n: u128) -> usize {
+    let mut i = 0;
+    if n == 0 {
+        return 1;
+    }
+    while n > 0 {
+        n = n / 10;
+        i += 1;
+    }
+    i
+}
+
+pub(crate) const fn static_int_str_array<const RES: usize>(mut n: u128) -> [u8; RES] {
+    let mut res: [u8; RES] = [0; RES];
+    let mut i = 0;
+    if n == 0 {
+        res[0] = '0' as u8;
+        return res;
+    }
+    while n > 0 {
+        res[i] = '0' as u8 + (n % 10) as u8;
+        n = n / 10;
+        i += 1;
+    }
+
+    let mut rev: [u8; RES] = [0; RES];
+    let mut rev_i = 0;
+    while 0 < i {
+        i -= 1;
+        rev[rev_i] = res[i];
+        n = n / 10;
+        rev_i += 1;
+    }
+    rev
+}
+
+pub(crate) const fn static_encoding_str_len(encoding: Encoding<'_>) -> usize {
+    use Encoding::*;
+
+    match encoding {
+        Char | Short | Int | Long | LongLong | UChar | UShort | UInt | ULong | ULongLong
+        | Float | Double | LongDouble | Bool | Void | String | Object | Class | Sel | Unknown => 1,
+        Block | FloatComplex | DoubleComplex | LongDoubleComplex => 2,
+        BitField(b, _type) => 1 + static_int_str_len(b as u128),
+        Pointer(&t) => 1 + static_encoding_str_len(t),
+        Array(len, &item) => {
+            1 + static_int_str_len(len as u128) + static_encoding_str_len(item) + 1
+        }
+        Struct(name, items) | Union(name, items) => {
+            let mut res = 1 + name.len() + 1;
+            let mut i = 0;
+            while i < items.len() {
+                res += static_encoding_str_len(items[i]);
+                i += 1;
+            }
+            res + 1
+        }
+    }
+}
+
+pub(crate) const fn static_encoding_str_array<const LEN: usize>(
+    encoding: Encoding<'_>,
+) -> [u8; LEN] {
+    use Encoding::*;
+
+    let mut res: [u8; LEN] = [0; LEN];
+
+    match encoding {
+        Char => res[0] = 'c' as u8,
+        Short => res[0] = 's' as u8,
+        Int => res[0] = 'i' as u8,
+        Long => res[0] = 'l' as u8,
+        LongLong => res[0] = 'q' as u8,
+        UChar => res[0] = 'C' as u8,
+        UShort => res[0] = 'S' as u8,
+        UInt => res[0] = 'I' as u8,
+        ULong => res[0] = 'L' as u8,
+        ULongLong => res[0] = 'Q' as u8,
+        Float => res[0] = 'f' as u8,
+        Double => res[0] = 'd' as u8,
+        LongDouble => res[0] = 'D' as u8,
+        FloatComplex => {
+            res[0] = 'j' as u8;
+            res[1] = 'f' as u8;
+        }
+        DoubleComplex => {
+            res[0] = 'j' as u8;
+            res[1] = 'd' as u8;
+        }
+        LongDoubleComplex => {
+            res[0] = 'j' as u8;
+            res[1] = 'D' as u8;
+        }
+        Bool => res[0] = 'B' as u8,
+        Void => res[0] = 'v' as u8,
+        Block => {
+            res[0] = '@' as u8;
+            res[1] = '?' as u8;
+        }
+        String => res[0] = '*' as u8,
+        Object => res[0] = '@' as u8,
+        Class => res[0] = '#' as u8,
+        Sel => res[0] = ':' as u8,
+        Unknown => res[0] = '?' as u8,
+        BitField(b, &_type) => {
+            let mut res_i = 0;
+
+            res[res_i] = 'b' as u8;
+            res_i += 1;
+
+            let mut i = 0;
+            // We use 3 even though it creates an oversized array
+            let arr = static_int_str_array::<3>(b as u128);
+            while i < static_int_str_len(b as u128) {
+                res[res_i] = arr[i];
+                res_i += 1;
+                i += 1;
+            }
+        }
+        Pointer(&t) => {
+            let mut res_i = 0;
+
+            res[res_i] = '^' as u8;
+            res_i += 1;
+
+            let mut i = 0;
+            // We use LEN even though it creates an oversized array
+            let arr = static_encoding_str_array::<LEN>(t);
+            while i < static_encoding_str_len(t) {
+                res[res_i] = arr[i];
+                res_i += 1;
+                i += 1;
+            }
+        }
+        Array(len, &item) => {
+            let mut res_i = 0;
+
+            res[res_i] = '[' as u8;
+            res_i += 1;
+
+            let mut i = 0;
+            // We use 20 even though it creates an oversized array
+            let arr = static_int_str_array::<20>(len as u128);
+            while i < static_int_str_len(len as u128) {
+                res[res_i] = arr[i];
+                res_i += 1;
+                i += 1;
+            }
+
+            let mut i = 0;
+            // We use LEN even though it creates an oversized array
+            let arr = static_encoding_str_array::<LEN>(item);
+            while i < static_encoding_str_len(item) {
+                res[res_i] = arr[i];
+                res_i += 1;
+                i += 1;
+            }
+
+            res[res_i] = ']' as u8;
+        }
+        Struct(name, items) | Union(name, items) => {
+            let mut res_i = 0;
+
+            match encoding {
+                Struct(_, _) => res[res_i] = '{' as u8,
+                Union(_, _) => res[res_i] = '(' as u8,
+                _ => {}
+            };
+            res_i += 1;
+
+            let mut name_i = 0;
+            let name = name.as_bytes();
+            while name_i < name.len() {
+                res[res_i] = name[name_i];
+                res_i += 1;
+                name_i += 1;
+            }
+
+            res[res_i] = '=' as u8;
+            res_i += 1;
+
+            let mut items_i = 0;
+            while items_i < items.len() {
+                // We use LEN even though it creates an oversized array
+                let field_res = static_encoding_str_array::<LEN>(items[items_i]);
+
+                let mut item_res_i = 0;
+                while item_res_i < static_encoding_str_len(items[items_i]) {
+                    res[res_i] = field_res[item_res_i];
+                    res_i += 1;
+                    item_res_i += 1;
+                }
+                items_i += 1;
+            }
+
+            match encoding {
+                Struct(_, _) => res[res_i] = '}' as u8,
+                Union(_, _) => res[res_i] = ')' as u8,
+                _ => {}
+            };
+        }
+    };
+    res
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    macro_rules! const_int_str {
+        ($n:expr) => {{
+            const X: [u8; static_int_str_len($n as u128)] = static_int_str_array($n as u128);
+            unsafe { core::mem::transmute::<&[u8], &str>(&X) }
+        }};
+    }
+
+    #[test]
+    fn test_const_int_str() {
+        const STR_0: &'static str = const_int_str!(0);
+        const STR_4: &'static str = const_int_str!(4);
+        const STR_42: &'static str = const_int_str!(42);
+        const STR_100: &'static str = const_int_str!(100);
+        const STR_999: &'static str = const_int_str!(999);
+        const STR_1236018655: &'static str = const_int_str!(1236018655);
+
+        assert_eq!(STR_0, "0");
+        assert_eq!(STR_4, "4");
+        assert_eq!(STR_42, "42");
+        assert_eq!(STR_100, "100");
+        assert_eq!(STR_999, "999");
+        assert_eq!(STR_1236018655, "1236018655");
+    }
+
+    macro_rules! const_encoding {
+        ($e:expr) => {{
+            const E: $crate::Encoding<'static> = $e;
+            const X: [u8; static_encoding_str_len(E)] = static_encoding_str_array(E);
+            unsafe { core::mem::transmute::<&'static [u8], &'static str>(&X) }
+        }};
+    }
+
+    #[test]
+    fn test_const_encoding() {
+        const CHAR: &'static str = const_encoding!(Encoding::Char);
+        assert_eq!(CHAR, "c");
+        const BLOCK: &'static str = const_encoding!(Encoding::Block);
+        assert_eq!(BLOCK, "@?");
+        const STRUCT: &'static str =
+            const_encoding!(Encoding::Struct("abc", &[Encoding::Int, Encoding::Double]));
+        assert_eq!(STRUCT, "{abc=id}");
+        const VARIOUS: &'static str = const_encoding!(Encoding::Struct(
+            "abc",
+            &[
+                Encoding::Pointer(&Encoding::Array(8, &Encoding::Bool)),
+                Encoding::Union("def", &[Encoding::Block]),
+                Encoding::Pointer(&Encoding::Pointer(&Encoding::BitField(255, &Encoding::Int))),
+                Encoding::Unknown,
+            ]
+        ));
+        assert_eq!(VARIOUS, "{abc=^[8B](def=@?)^^b255?}");
+    }
+}