Use derive_const in nightly feature

src/lib.rs

@@ -60,6 +60,8 @@ pub use seeded_state::{FxHashMapSeed, FxHashSetSeed};
 /// The current implementation is a fast polynomial hash with a single
 /// bit rotation as a finishing step designed by Orson Peters.
 #[derive(Clone)]
+#[cfg_attr(not(feature = "nightly"), derive(Default))]
+#[cfg_attr(feature = "nightly", derive_const(Default))]
 pub struct FxHasher {
     hash: usize,
 }
@@ -90,34 +92,6 @@ impl FxHasher {
     }
 }
 
-#[cfg(not(feature = "nightly"))]
-macro_rules! default_impl {
-    () => {
-        impl Default for FxHasher {
-            #[inline]
-            fn default() -> FxHasher {
-                Self::default()
-            }
-        }
-    };
-}
-
-// In order to use the nightly-only `const` syntax, we gate the definition behind a macro so that
-// parsing still succeeds on stable.
-#[cfg(feature = "nightly")]
-macro_rules! default_impl {
-    () => {
-        impl const Default for FxHasher {
-            #[inline]
-            fn default() -> FxHasher {
-                Self::default()
-            }
-        }
-    };
-}
-
-default_impl!();
-
 impl FxHasher {
     #[inline]
     fn add_to_hash(&mut self, i: usize) {

src/random_state.rs

@@ -92,7 +92,7 @@ mod tests {
         // `1 / 2.pow(bit_size_of::<usize>())`. Or 1/1.7e19 for 64 bit platforms or 1/4294967295
         // for 32 bit platforms. I suppose this is acceptable.
         let a = FxHashMapRand::<&str, u32>::default();
-        let b = thread::spawn(|| FxHashMapRand::<&str, u32>::default())
+        let b = thread::spawn(FxHashMapRand::<&str, u32>::default)
             .join()
             .unwrap();