WIP: progress on Bound function

src/BoundFunction.zig

@@ -1,36 +1,148 @@
 const std = @import("std");
 
-// attempt 1: explicitly typed
-pub fn Create(Fn: type, Instance: type) type {
+/// Bind a function with specific signature to a method of any instance of a given type
+pub fn OldBind(func: anytype, instance: anytype) OldBound(@typeInfo(@TypeOf(instance)).pointer.child, func) {
+    const Instance = @typeInfo(@TypeOf(instance)).pointer.child;
+    return OldBound(Instance, func).init(@constCast(instance));
+}
+
+pub fn OldBound(Instance: type, func: anytype) type {
+    // Verify Func is a function type
+    const func_info = @typeInfo(@TypeOf(func));
+    if (func_info != .@"fn") {
+        @compileError("OldBound expexts a function type as second parameter");
+    }
+
+    // Verify first parameter is pointer to Instance type
+    const params = func_info.@"fn".params;
+    if (params.len == 0 or (params[0].type != *Instance and params[0].type != *const Instance)) {
+        @compileError("Function's first parameter must be " ++ @typeName(Instance) ++ " but got: " ++ @typeName(params[0].type.?));
+    }
+
     return struct {
         instance: *Instance,
-        function: *const Fn,
+
+        const OldBoundFunction = @This();
+
+        pub fn call(self: OldBoundFunction, args: anytype) func_info.@"fn".return_type.? {
+            return @call(.auto, func, .{self.instance} ++ args);
+        }
+
+        // convenience init
+        pub fn init(instance_: *Instance) OldBoundFunction {
+            return .{ .instance = instance_ };
+        }
+    };
+}
+
+test "OldBound" {
+    const Person = struct {
+        name: []const u8,
+        _buf: [1024]u8 = undefined,
+
+        // takes const instance
+        pub fn greet(self: *const @This(), gpa: std.mem.Allocator, greeting: []const u8) ![]const u8 {
+            return std.fmt.allocPrint(gpa, "{s}, {s}!\n", .{ greeting, self.name });
+        }
+
+        // takes non-const instance
+        pub fn farewell(self: *@This(), message: []const u8) ![]const u8 {
+            return std.fmt.bufPrint(self._buf[0..], "{s}, {s}!\n", .{ message, self.name });
+        }
+    };
+
+    var alice: Person = .{ .name = "Alice" };
+
+    // creation variant a: manually instantiate
+    const bound_greet: OldBound(Person, Person.greet) = .{ .instance = &alice };
+
+    // creation variant b: call init function
+    const bound_farewell = OldBound(Person, Person.farewell).init(&alice);
+
+    const ta = std.testing.allocator;
+    const greeting = try bound_greet.call(.{ ta, "Hello" });
+    defer ta.free(greeting);
+
+    try std.testing.expectEqualStrings("Hello, Alice!\n", greeting);
+    try std.testing.expectEqualStrings("Goodbye, Alice!\n", try bound_farewell.call(.{"Goodbye"}));
+}
+
+test OldBind {
+    const Person = struct {
+        name: []const u8,
+        _buf: [1024]u8 = undefined,
+
+        // takes const instance
+        pub fn greet(self: *const @This(), gpa: std.mem.Allocator, greeting: []const u8) ![]const u8 {
+            return std.fmt.allocPrint(gpa, "{s}, {s}!\n", .{ greeting, self.name });
+        }
+
+        // takes non-const instance
+        pub fn farewell(self: *@This(), message: []const u8) ![]const u8 {
+            return std.fmt.bufPrint(self._buf[0..], "{s}, {s}!\n", .{ message, self.name });
+        }
+    };
+
+    var alice: Person = .{ .name = "Alice" };
+
+    const bound_greet = OldBind(Person.greet, &alice);
+    const bound_farewell = OldBind(Person.farewell, &alice);
+
+    const ta = std.testing.allocator;
+    const greeting = try bound_greet.call(.{ ta, "Hello" });
+    defer ta.free(greeting);
+
+    try std.testing.expectEqualStrings("Hello, Alice!\n", greeting);
+    try std.testing.expectEqualStrings("Goodbye, Alice!\n", try bound_farewell.call(.{"Goodbye"}));
+}
+
+/// Bind functions like `fn(a: X, b: Y)` to an instance of a struct. When called, the instance's `pub fn(self: *This(), a: X, b: Y)` is called.
+///
+/// make callbacks stateful when they're not meant to be?
+// pub fn Bound(Instance: type, Func: type, func: anytype) type {
+pub fn Bound(Instance: type, Func: type, DFunc: type) type {
+
+    // TODO: construct DFunc on-the-fly
+
+    // Verify Func is a function type
+    const func_info = @typeInfo(Func);
+    // if (func_info != .@"fn") {
+    //     @compileError("Bound expexts a function type as second parameter");
+    // }
+    return struct {
+        instance: *Instance,
+        foo: *const DFunc,
 
         const BoundFunction = @This();
 
-        pub fn init(function: *const Fn, instance: *Instance) BoundFunction {
-            return .{
-                .instance = instance,
-                .function = function,
-            };
+        pub fn call(self: BoundFunction, args: anytype) func_info.@"fn".return_type.? {
+            return @call(.auto, self.foo, .{self.instance} ++ args);
         }
 
-        pub fn call(self: *const BoundFunction, arg: anytype) void {
-            @call(.auto, self.function, .{ self.instance, arg });
+        // convenience init
+        pub fn init(instance_: *Instance, foo_: *const DFunc) BoundFunction {
+            return .{ .instance = instance_, .foo = foo_ };
         }
     };
 }
 
-test "BoundFunction" {
-    const X = struct {
-        field: usize = 0,
-        pub fn foo(self: *@This(), other: usize) void {
-            std.debug.print("field={d}, other={d}\n", .{ self.field, other });
+test Bound {
+    const Person = struct {
+        name: []const u8,
+        _buf: [1024]u8 = undefined,
+
+        pub fn speak(self: *@This(), message: []const u8) ![]const u8 {
+            return std.fmt.bufPrint(self._buf[0..], "{s} says: >>{s}!<<\n", .{ self.name, message });
         }
     };
 
-    var x: X = .{ .field = 27 };
+    const CallBack = fn ([]const u8) anyerror![]const u8;
 
-    var bound = Create(@TypeOf(X.foo), X).init(X.foo, &x);
-    bound.call(3);
+    var alice: Person = .{ .name = "Alice" };
+
+    const bound_greet = Bound(Person, CallBack, @TypeOf(Person.speak)).init(&alice, &Person.speak);
+
+    const greeting = try bound_greet.call(.{"Hello"});
+
+    try std.testing.expectEqualStrings("Alice says: >>Hello!<<\n", greeting);
 }