Tiles & Melds

This page covers the value and instance types that make up a hand: Tile → GameTile → MenLike → Hand.

Tile — a tile kind (value type)

Core/Tile.cs defines struct Tile, an 8-bit packed value type. It represents a kind of tile (e.g. "5 pin"), not a specific physical tile on the table.

• Packing: bits 0–3 = number (1–9), bits 4–6 = suit, bit 7 = akadora flag.
• Key statics: Tile.Empty (the invalid/"back" tile) and Tile.North (used for nukidora).
• Predicates: IsValid, IsEmpty, Is19Z (terminal/honor), IsZ, IsMPS, IsSangen (dragon), IsWind.
• Equality: == compares the raw byte (so a red five differs from a normal five), while IsSame ignores the red-five bit — that's the usual "same kind" comparison.
• Sequences: Prev / Next give neighbours within a suit; IsNext / IsPrev test adjacency.
• Dora: NextDora maps a dora indicator to the actual dora tile, with the correct wrap-arounds (9→1 for suits, N→E for winds, Red→White for dragons).

Tiles : List<Tile> is a collection with the multi-tile string parser, a compact ToString(), and meld classifiers (IsKou, IsKan, IsShun, IsJan). Handy static sets include Tiles.All (the full 136-tile set with one red five per suit — the default wall contents), Tiles.T19Z, and Tiles.T19.

See Tile notation for the parsing grammar.

GameTile — a physical tile instance

Core/GameTile.cs defines GameTile, a trackable physical tile that wraps a Tile and carries per-instance metadata:

Member	Meaning
tile	The underlying Tile kind.
traceId	A random id, unique within a round, that follows this physical tile. Reset when it re-enters the wall.
player / playerId	Current owner (set on discard/meld).
discardInfo	If discarded: who discarded it, why (DiscardReason), when, and on which jun.
drawnJun	The turn it was drawn into hand. Comparing drawnJun with a discard's jun distinguishes tedashi (手切り) from tsumogiri (摸切り).
source	Where it currently is (Hand, Wall, Wanpai, Discard, …).
IsTsumo	discardInfo == null — i.e. self-drawn / concealed.

traceId is the stable handle clients and replays use to follow a specific tile across events. GameTile also supports Freeze() (an internal Refrigerator) to snapshot and restore its mutable fields for hypothetical evaluation — the engine uses this while probing pattern/shanten alternatives without mutating game state.

MenLike — a meld / group

Core/MenLike.cs defines the abstract MenLike (a read-only, sorted collection of GameTiles) and its concrete subtypes:

Type	Shape	Example
Shun	Sequence (順子)
Kou	Triplet (刻子)
Kan	Quad (槓)
Jantou	The pair (雀頭)
Musou	A single tile (only used by Thirteen Orphans)

Notable members:

• Value — a canonical id that ignores red fives (used to compare melds).
• IsClose — true when every tile is concealed/self-drawn (matters for scoring, e.g. a concealed triplet).
• Kan.KanSource — auto-detected: ankan (all closed), kakan (added to a pon), or daiminkan (called).
• MenLike.From(...) — a factory that builds the right subtype from tiles.

Hand — one player's hand

Core/Hand.cs holds everything about a single player's hand during a round:

Tiles

• freeTiles — the concealed tiles (excluding melds).
• pendingTile — the just-drawn tile, if any.
• called — the list of melds (MenLike).
• discarded — the discard pond (牌河).
• nukiDora — pulled North tiles (拔北); +1 han each, not counted in hand size.

State

• jun — the hand's turn counter.
• Riichi: riichiTile, riichi, wRiichi (double riichi), ippatsu.
• menzen — closed-hand status.
• Agari: agariTile, agari.
• Furiten: isTempFuriten, isRiichiFuriten, isDiscardFuriten, combined isFuriten.
• Tenpai — the current waits (computed via the PatternResolver when the hand is at 13 tiles).
• Count — total tiles, where a kan counts as 3.

Mutations (used by event listeners, not usually by you directly): AddPending, Riichi, Play (discard), AddChii / AddPon / AddKan, Kakan, and Nuki.

Winning-tile grouping matters

The same 14 tiles can often be grouped more than one way, and the grouping can change the fu (and occasionally the yaku). That's why scoring enumerates all decompositions and keeps the highest — see Patterns & scoring.