Add initialization functions for stack data structures

src/stack.zig

@@ -18,8 +18,8 @@ pub const FinitePushError = error {
 ///
 pub fn Fixed(comptime Element: type, comptime capacity: usize) type {
     return struct {
-        filled: usize = 0,
-        buffer: [capacity]Element = undefined,
+        filled: usize,
+        buffer: [capacity]Element,
 
         const Self = @This();
 
@@ -57,6 +57,16 @@ pub fn Fixed(comptime Element: type, comptime capacity: usize) type {
             return self.filled;
         }
 
+        ///
+        /// Creates and returns a [Self] value.
+        ///
+        pub fn init() Self {
+            return Self{
+                .filled = 0,
+                .buffer = undefined,
+            };
+        }
+
         ///
         /// Attempts to pop the tail-end of `self`, returning the element value or `null` if the
         /// stack is empty.
@@ -137,6 +147,16 @@ pub fn Unmanaged(comptime Element: type) type {
             return self.filled;
         }
 
+        ///
+        /// Creates and returns a [Self] value wrapping `buffer` as its writable memory buffer.
+        ///
+        pub fn init(buffer: []Element) Self {
+            return Self{
+                .filled = 0,
+                .buffer = buffer,
+            };
+        }
+
         ///
         /// Attempts to pop the tail-end of `self`, returning the element value or `null` if the
         /// stack is empty.