Use metavar ${count(x)} instead of reimplementing it

Author: WaffleLapkin

library/core/src/tuple.rs

@@ -102,17 +102,17 @@ macro_rules! tuple_impls {
         }
 
         #[stable(feature = "array_tuple_conv", since = "1.63.0")]
-        impl<T> From<[T; count!($($T)+)]> for ($(${ignore(T)} T,)+) {
+        impl<T> From<[T; ${count(T)}]> for ($(${ignore(T)} T,)+) {
             #[inline]
             #[allow(non_snake_case)]
-            fn from(array: [T; count!($($T)+)]) -> Self {
+            fn from(array: [T; ${count(T)}]) -> Self {
                 let [$($T,)+] = array;
                 ($($T,)+)
             }
         }
 
         #[stable(feature = "array_tuple_conv", since = "1.63.0")]
-        impl<T> From<($(${ignore(T)} T,)+)> for [T; count!($($T)+)] {
+        impl<T> From<($(${ignore(T)} T,)+)> for [T; ${count(T)}] {
             #[inline]
             #[allow(non_snake_case)]
             fn from(tuple: ($(${ignore(T)} T,)+)) -> Self {
@@ -200,12 +200,6 @@ macro_rules! last_type {
 
 tuple_impls!(E D C B A Z Y X W V U T);
 
-macro_rules! count {
-    ($($a:ident)*) => {
-        0 $(${ignore(a)} + 1)*
-    };
-}
-
 #[stable(feature = "array_tuple_conv", since = "1.63.0")]
 impl<T> From<()> for [T; 0] {
     fn from((): ()) -> Self {