Update outdated FIXME

src/identities.rs

@@ -17,7 +17,7 @@ pub trait Zero: Sized + Add<Self, Output = Self> {
     /// This function should return the same result at all times regardless of
     /// external mutable state, for example values stored in TLS or in
     /// `static mut`s.
-    // FIXME (#5527): This should be an associated constant
+    // This cannot be an associated constant, because of bignums.
     fn zero() -> Self;
 
     /// Returns `true` if `self` is equal to the additive identity.
@@ -77,7 +77,7 @@ pub trait One: Sized + Mul<Self, Output = Self> {
     /// This function should return the same result at all times regardless of
     /// external mutable state, for example values stored in TLS or in
     /// `static mut`s.
-    // FIXME (#5527): This should be an associated constant
+    // This cannot be an associated constant, because of bignums.
     fn one() -> Self;
 
     /// Returns `true` if `self` is equal to the multiplicative identity.