[Breaking] Add MAX_LENGTH associated constant

src/lib.rs

@@ -22,6 +22,12 @@ mod macros;
 
 /// A no-alloc version of [`ToString`] implemented for bool/integer/float types formatting into an [`ArrayString`].
 pub trait ToArrayString: Copy {
+    /// The maximum length that Self can be formatted into. This is used for the capacity generic of [`ArrayString`].
+    ///
+    /// # Note for implementors
+    /// This must match the capacity generic used in [`ArrayString`], otherwise logic bugs and panics may occur.
+    const MAX_LENGTH: usize;
+
     /// An associated type to turn [`ArrayString`]'s const generic into a type generic,
     /// working around limitations of the current type system.
     ///
@@ -33,6 +39,7 @@ pub trait ToArrayString: Copy {
 }
 
 impl<const MAX_LENGTH: usize> ToArrayString for ArrayString<MAX_LENGTH> {
+    const MAX_LENGTH: usize = MAX_LENGTH;
     type ArrayString = ArrayString<MAX_LENGTH>;
 
     fn to_arraystring(self) -> Self::ArrayString {
@@ -41,6 +48,7 @@ impl<const MAX_LENGTH: usize> ToArrayString for ArrayString<MAX_LENGTH> {
 }
 
 impl ToArrayString for char {
+    const MAX_LENGTH: usize = 4;
     type ArrayString = ArrayString<4>;
 
     fn to_arraystring(self) -> Self::ArrayString {
@@ -52,6 +60,7 @@ impl ToArrayString for char {
 }
 
 impl ToArrayString for bool {
+    const MAX_LENGTH: usize = 5;
     type ArrayString = ArrayString<5>;
 
     fn to_arraystring(self) -> Self::ArrayString {

src/macros.rs

@@ -14,7 +14,9 @@ macro_rules! gen_impl {
         macro_rules! $name {
             (ToArrayString<$len:literal> for $type:ty) => {
                 impl ToArrayString for $type {
+                    const MAX_LENGTH: usize = $len;
                     type ArrayString = ArrayString<$len>;
+
                     fn to_arraystring(self) -> Self::ArrayString {
                         $body(self)
                     }