Allow fibers as map keys.

doc/site/maps.markdown

@@ -17,7 +17,9 @@ curly braces. Each entry is a key and a value separated by a colon:
     }
 
 This creates a map that maps the first names of the Beatles to their last
-names. Syntactically, in a map literal, keys can be any literal, a variable name, or a parenthesized expression. Values can be any expression. Here, we're using string literals for both keys and values.
+names. Syntactically, in a map literal, keys can be any literal, a variable
+name, or a parenthesized expression. Values can be any expression. Here, we're
+using string literals for both keys and values.
 
 *Semantically*, values can be any object, and multiple keys may map to the
 same value. Keys have a few limitations. They must be one of the immutable
@@ -25,7 +27,15 @@ built-in [value types](values.html) in Wren. That means a number, string,
 range, bool, or `null`. You can also use a [class object](classes.html) as a
 key.
 
-The reason for this limitation—and the reason maps are called "*hash* tables" in other languages—is that each key is used to generate a numeric *hash code*. This lets a map locate the value associated with a key in constant time, even in very large maps. Since Wren only knows how to hash certain built-in types, only those can be used as keys.
+In addition, even though they aren't strictly immutable, [fibers](fibers.html)
+can be used as map keys. This is handy for storing data that's roughly
+"thread-local" by using the current fiber as a map key.
+
+The reason for this limitation—and the reason maps are called "*hash*
+tables" in other languages—is that each key is used to generate a numeric
+*hash code*. This lets a map locate the value associated with a key in constant
+time, even in very large maps. Since Wren only knows how to hash certain
+built-in types, only those can be used as keys.
 
 ## Adding entries
 
@@ -37,18 +47,22 @@ You add new key-value pairs to the map by using the [subscript operator][]:
     capitals["Idaho"] = "Boise"
     capitals["Maine"] = "Augusta"
 
-If the key isn't already present, this adds it and associates it with the given value. If the key is already there, this just replaces its value.
+If the key isn't already present, this adds it and associates it with the given
+value. If the key is already there, this just replaces its value.
 
 [subscript operator]: expressions.html#subscript-operators
 
 ## Looking up values
 
-To find the value associated with some key, again you use your friend the subscript operator:
+To find the value associated with some key, again you use your friend the
+subscript operator:
 
     :::dart
     IO.print(capitals["Idaho"]) // "Boise".
 
-If the key is present, this returns its value. Otherwise, it returns `null`. Of course, `null` itself can also be used as a value, so seeing `null` here doesn't necessarily mean the key wasn't found.
+If the key is present, this returns its value. Otherwise, it returns `null`. Of
+course, `null` itself can also be used as a value, so seeing `null` here
+doesn't necessarily mean the key wasn't found.
 
 To tell definitively if a key exists, you can call `containsKey()`:
 
@@ -67,7 +81,8 @@ You can see how many entries a map contains using `count`:
 
 ## Removing entries
 
-To remove an entry from a map, call `remove()` and pass in the key for the entry you want to delete:
+To remove an entry from a map, call `remove()` and pass in the key for the
+entry you want to delete:
 
     :::dart
     capitals.remove("Maine")
@@ -91,14 +106,18 @@ can just call `clear()`:
 
 ## Iterating over the contents
 
-The subscript operator works well for finding values when you know the key you're looking for, but sometimes you want to see everything that's in the map. For that, map exposes two methods: `keys` and `values`.
+The subscript operator works well for finding values when you know the key
+you're looking for, but sometimes you want to see everything that's in the map.
+For that, map exposes two methods: `keys` and `values`.
 
-The first returns a [Sequence][] that [iterates][] over all of the keys in the map, and the second returns one that iterates over the values.
+The first returns a [Sequence][] that [iterates][] over all of the keys in the
+map, and the second returns one that iterates over the values.
 
 [sequence]: core/sequence.html
 [iterates]: control-flow.html#the-iterator-protocol
 
-If you want to see all of the key-value pairs in a map, the easiest way is to iterate over the keys and use each to look up its value:
+If you want to see all of the key-value pairs in a map, the easiest way is to
+iterate over the keys and use each to look up its value:
 
     :::dart
     var stateBirds = {
@@ -111,4 +130,7 @@ If you want to see all of the key-value pairs in a map, the easiest way is to it
       IO.print("The state bird of ", state, " is ", stateBirds[state])
     }
 
-This program will print the three states and their birds. However, the *order* that they are printed isn't defined. Wren makes no promises about what order keys and values will be iterated in when you use these methods. All it promises is that every entry will appear exactly once.
+This program will print the three states and their birds. However, the *order*
+that they are printed isn't defined. Wren makes no promises about what order
+keys and values will be iterated in when you use these methods. All it promises
+is that every entry will appear exactly once.

src/vm/wren_primitive.c

@@ -53,13 +53,13 @@ uint32_t validateIndexValue(WrenVM* vm, Value* args, uint32_t count,
 bool validateKey(WrenVM* vm, Value* args, int index)
 {
   Value arg = args[index];
-  if (IS_BOOL(arg) || IS_CLASS(arg) || IS_NULL(arg) ||
+  if (IS_BOOL(arg) || IS_CLASS(arg) || IS_FIBER(arg) || IS_NULL(arg) ||
       IS_NUM(arg) || IS_RANGE(arg) || IS_STRING(arg))
   {
     return true;
   }
 
-  args[0] = CONST_STRING(vm, "Key must be a value type.");
+  args[0] = CONST_STRING(vm, "Key must be a value type or fiber.");
   return false;
 }
 

src/vm/wren_value.c

@@ -136,6 +136,7 @@ ObjFiber* wrenNewFiber(WrenVM* vm, Obj* fn)
 {
   ObjFiber* fiber = ALLOCATE(vm, ObjFiber);
   initObj(vm, &fiber->obj, OBJ_FIBER, vm->fiberClass);
+  fiber->id = vm->nextFiberId++;
 
   wrenResetFiber(fiber, fn);
 
@@ -322,6 +323,9 @@ static uint32_t hashObject(Obj* object)
       // Classes just use their name.
       return hashObject((Obj*)((ObjClass*)object)->name);
 
+    case OBJ_FIBER:
+      return ((ObjFiber*)object)->id;
+
     case OBJ_RANGE:
     {
       ObjRange* range = (ObjRange*)object;

src/vm/wren_value.h

@@ -133,7 +133,8 @@ typedef enum
 typedef struct
 {
   ValueType type;
-  union {
+  union
+  {
     double num;
     Obj* obj;
   } as;
@@ -226,6 +227,10 @@ typedef struct sObjFiber
   // error message. Otherwise, it will be NULL.
   ObjString* error;
 
+  // A unique-ish numeric ID for the fiber. Lets fibers be used as map keys.
+  // Unique-ish since IDs may overflow and wrap around.
+  uint16_t id;
+
   // This will be true if the caller that called this fiber did so using "try".
   // In that case, if this fiber fails with an error, the error will be given
   // to the caller.

src/vm/wren_vm.h

@@ -50,6 +50,11 @@ struct WrenVM
   // for the module.
   ObjMap* modules;
 
+  // The ID that will be assigned to the next fiber that is allocated. Fibers
+  // are given unique-ish (not completely unique since this can overflow) IDs
+  // so that they can be used as map keys.
+  uint16_t nextFiberId;
+
   // Memory management data:
 
   // The externally-provided function used to allocate memory.

test/core/map/contains_key_not_value.wren

@@ -1 +1 @@
-var result = {}.containsKey([]) // expect runtime error: Key must be a value type.
+var result = {}.containsKey([]) // expect runtime error: Key must be a value type or fiber.

test/core/map/key_types.wren

@@ -1,3 +1,5 @@
+var fiber = new Fiber {}
+
 var map = {
   null: "null value",
   true: "true value",
@@ -6,7 +8,8 @@ var map = {
   1.2: "1 point 2",
   List: "list class",
   "null": "string value",
-  (1..3): "1 to 3"
+  (1..3): "1 to 3",
+  fiber: "fiber"
 }
 
 IO.print(map[null]) // expect: null value
@@ -17,8 +20,9 @@ IO.print(map[1.2]) // expect: 1 point 2
 IO.print(map[List]) // expect: list class
 IO.print(map["null"]) // expect: string value
 IO.print(map[1..3]) // expect: 1 to 3
+IO.print(map[fiber]) // expect: fiber
 
-IO.print(map.count) // expect: 8
+IO.print(map.count) // expect: 9
 
 // Use the same keys (but sometimes different objects) to ensure keys have the
 // right equality semantics.
@@ -40,4 +44,4 @@ IO.print(map[List]) // expect: new list class
 IO.print(map["null"]) // expect: new string value
 IO.print(map[1..3]) // expect: new 1 to 3
 
-IO.print(map.count) // expect: 8
+IO.print(map.count) // expect: 9

test/core/map/remove_key_not_value.wren

@@ -1 +1 @@
-var result = {}.remove([]) // expect runtime error: Key must be a value type.
+var result = {}.remove([]) // expect runtime error: Key must be a value type or fiber.

test/core/map/subscript_key_not_value.wren

@@ -1 +1 @@
-var result = {}[[]] // expect runtime error: Key must be a value type.
+var result = {}[[]] // expect runtime error: Key must be a value type or fiber.

test/core/map/subscript_setter_key_not_value.wren

@@ -1 +1 @@
-var result = {}[[]] = "value" // expect runtime error: Key must be a value type.
+var result = {}[[]] = "value" // expect runtime error: Key must be a value type or fiber.