initial commit

1 files changed, 51 insertions, 0 deletions

diff --git a/src/peek.zig b/src/peek.zig
new file mode 100644
index 0000000..58911e9
--- /dev/null
+++ b/src/peek.zig
@@ -0,0 +1,51 @@
+pub fn peekable(iterator: anytype) Peekable(@TypeOf(iterator)) {
+    return .{ .iterator = iterator };
+}
+
+pub fn Peekable(Iterator: type) type {
+    const ActualIterator = switch (@typeInfo(Iterator)) {
+        .pointer => |p| p.child,
+        else => Iterator,
+    };
+    const Next = @typeInfo(@TypeOf(ActualIterator.next)).@"fn";
+    const Item = switch (@typeInfo(Next.return_type.?)) {
+        .optional => |o| o.child,
+        else => |i| i,
+    };
+    return struct {
+        iterator: Iterator,
+        peeked: ?Item = null,
+
+        pub fn peek(self: *Self) ?Item {
+            if (self.peeked) |peeked| return peeked;
+            const item = self.iterator.next();
+            self.peeked = item;
+            return item;
+        }
+
+        pub fn next(self: *Self) ?Item {
+            const item = if (self.peeked) |peeked| peeked else self.iterator.next();
+            self.peeked = null;
+            return item;
+        }
+
+        const Self = @This();
+    };
+}
+
+test peekable {
+    const expect = std.testing.expect;
+    // std.meta.de
+
+    var it = std.mem.window(u8, &[_]u8{ 1, 2, 3 }, 1, 1);
+    var peek = peekable(&it);
+    try expect(peek.next().?[0] == 1);
+    try expect(peek.peek().?[0] == 2);
+    try expect(peek.peek().?[0] == 2);
+    try expect(peek.next().?[0] == 2);
+    try expect(peek.next().?[0] == 3);
+    try expect(peek.peek() == null);
+    try expect(peek.next() == null);
+}
+
+const std = @import("std");