added dupe method

src/root.zig

@@ -1,5 +1,7 @@
 const std = @import("std");
 
+const AllocError = std.mem.Allocator.Error;
+
 pub const SmolStr = struct {
     pub const max_inline_len: usize = 22;
 
@@ -13,7 +15,7 @@ pub const SmolStr = struct {
 
     inner: Inner,
 
-    pub fn init(alloc: std.mem.Allocator, s: []const u8) !SmolStr {
+    pub fn init(alloc: std.mem.Allocator, s: []const u8) AllocError!SmolStr {
         if (s.len <= max_inline_len) {
             return initInline(s);
         }
@@ -73,6 +75,13 @@ pub const SmolStr = struct {
         }
     }
 
+    pub fn dupe(self: SmolStr, alloc: std.mem.Allocator) AllocError!SmolStr {
+        switch (self.inner) {
+            .inl => return self, // dupe inlined string by direct copy
+            .heap => |s| return try SmolStr.init(alloc, s),
+        }
+    }
+
     pub fn format(self: SmolStr, comptime fmt: []const u8, options: std.fmt.FormatOptions, writer: anytype) !void {
         _ = fmt;
         _ = options;

tests/root.zig

@@ -36,3 +36,35 @@ test "heap" {
     try std.testing.expectEqual(s.len, str.len());
     try std.testing.expectEqualStrings(s, str.str());
 }
+
+test "dupe inline" {
+    const alloc = std.testing.allocator;
+
+    {
+        const s = "abcd";
+
+        const str1 = try SmolStr.init(alloc, s);
+        defer str1.deinit(alloc);
+
+        const str2 = try str1.dupe(alloc);
+        defer str2.deinit(alloc);
+
+        try std.testing.expectEqualSlices(u8, std.mem.asBytes(&str1), std.mem.asBytes(&str2));
+    }
+
+    {
+        const s = "abcdefghijklmnopqrstuvwxyz";
+
+        const str1 = try SmolStr.init(alloc, s);
+        defer str1.deinit(alloc);
+
+        const str2 = try str1.dupe(alloc);
+        defer str2.deinit(alloc);
+
+        // try std.testing.expectEqualSlices(u8, std.mem.asBytes(&str1), std.mem.asBytes(&str2));
+
+        try std.testing.expectEqualStrings(str1.str(), str2.str());
+
+        try std.testing.expect(str1.inner.heap.ptr != str2.inner.heap.ptr);
+    }
+}