strengthen type on first element

Author: mstn

src/index.d.ts

@@ -2,6 +2,6 @@
 // N is the length of the array
 // T is the type of array elements
 export type FixedSizeArray<N extends number, T> = N extends 0 ? never[] : {
-    0: any;
+    0: T;
     length: N;
 } & ReadonlyArray<T>;

src/test.ts

@@ -4,11 +4,13 @@ let d: FixedSizeArray<2, string>;
 
 d = ['a', 'b']; // ok
 d[0] = 'a2'; // ok
+d[0] = 0; // type error
 d[1] = 'b2'; // type error, but it is wrong!
 d[2] = 'c2'; // type error
 d = ['a']; // type error
 d = ['a', 'b', 'c']; // type error
 d = ['a', true]; // type error
+d = [true, 'a']; // type error
 
 d.push('d'); // type error