Fix bugs in memory module and add unit tests

src/mem.zig

@@ -14,9 +14,6 @@ pub fn Spliterator(comptime Element: type) type {
         ///
         /// Returns `true` if there is more data to be processed, otherwise `false`.
         ///
-        /// Note that [Spliterator.next] implicitly calls this function to determine if it should
-        /// return another slice or `null`.
-        ///
         pub fn hasNext(self: Self) bool {
             return (self.source.len != 0);
         }
@@ -26,27 +23,55 @@ pub fn Spliterator(comptime Element: type) type {
         /// [Spliterator.delimiter], or `null` if there is no more data to be processed.
         ///
         pub fn next(self: *Self) ?[]const Element {
-            if (self.delimiter.len == 0) {
-                defer self.source = self.source[self.source.len .. 0];
+            if (!self.hasNext()) return null;
+
+            if (std.mem.indexOfPos(Element, self.source, 0, self.delimiter)) |index| {
+                defer self.source = self.source[(index + self.delimiter.len) .. self.source.len];
+
+                return self.source[0 .. index];
+            }
+
+            defer self.source = self.source[self.source.len .. self.source.len];
 
             return self.source;
         }
-
-            while (self.hasNext()) {
-                var cursor = @as(usize, 0);
-                var window = self.source[cursor .. (self.source.len - cursor)];
-
-                defer self.source = window;
-
-                if (std.mem.eql(Element, window, self.delimiter))
-                    return self.source[cursor .. self.delimiter.len];
-            }
-
-            return null;
-        }
     };
 }
 
+test {
+    const testing = std.testing;
+
+    // Single-character delimiter.
+    {
+        var spliterator = Spliterator(u8){
+            .source = "single.character.separated.hello.world",
+            .delimiter = ".",
+        };
+
+        const components = [_][]const u8{"single", "character", "separated", "hello", "world"};
+        var index = @as(usize, 0);
+
+        while (spliterator.next()) |split| : (index += 1) {
+            try testing.expect(std.mem.eql(u8, split, components[index]));
+        }
+    }
+
+    // Multi-character delimiter.
+    {
+        var spliterator = Spliterator(u8){
+            .source = "finding a needle in a needle stack",
+            .delimiter = "needle",
+        };
+
+        const components = [_][]const u8{"finding a ", " in a ", " stack"};
+        var index = @as(usize, 0);
+
+        while (spliterator.next()) |split| : (index += 1) {
+            try testing.expect(std.mem.eql(u8, split, components[index]));
+        }
+    }
+}
+
 ///
 /// Searches the slice of `Data` referenced by `data` for the first instance of `sought_datum`,
 /// returning its index or `null` if it could not be found.
@@ -56,3 +81,7 @@ pub fn findFirst(comptime Data: type, data: []const Data, sought_datum: Data) ?u
 
     return null;
 }
+
+test {
+    try std.testing.expectEqual(findFirst(u8, "1234567890", '7'), 6);
+}