feat: support vtable generation

.github/workflows/ci.yml

@@ -1,29 +1,28 @@
-
 name: CI
 on:
   push:
-    branches: [ main ]
+    branches: [main]
   pull_request:
-    branches: [ main ]
+    branches: [main]
 
 jobs:
   test-example:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        zig-version: ["0.14.1"]
+        zig-version: ["0.15.1"]
 
     steps:
       - uses: actions/checkout@v3
-      
+
       - name: Install Zig
         uses: goto-bus-stop/setup-zig@v2
         with:
           version: ${{ matrix.zig-version }}
 
       - name: Check Zig Version
         run: zig version
-          
+
       - name: Run tests
         run: zig build test

README.md

@@ -1,22 +1,32 @@
 # Zig Interfaces & Validation
 
-A compile-time interface checker for Zig that enables interface-based design
-with comprehensive type checking and detailed error reporting.
+A comprehensive interface system for Zig supporting both **compile-time
+validation** and **runtime polymorphism** through VTable generation.
 
 ## Features
 
-This library provides a way to define and verify interfaces in Zig at compile
-time. It supports:
+This library provides two complementary approaches to interface-based design in
+Zig:
 
-- Type-safe interface definitions with detailed error reporting
+**VTable-Based Runtime Polymorphism:**
+
+- **Automatic VTable wrapper generation**
+- Automatic VTable type generation from interface definitions
+- Runtime polymorphism with function pointer dispatch
+- Return interface types from functions and store in fields
+
+**Compile-Time Interface Validation:**
+
+- Zero-overhead generic functions with compile-time type checking
+- Detailed error reporting for interface mismatches
 - Interface embedding (composition)
 - Complex type validation including structs, enums, arrays, and slices
-- Comprehensive compile-time error messages with helpful hints
 - Flexible error union compatibility with `anyerror`
 
 ## Install
 
-Add or update this library as a dependency in your zig project run the following command:
+Add or update this library as a dependency in your zig project run the following
+command:
 
 ```sh
 zig fetch --save git+https://github.com/nilslice/zig-interface
@@ -48,27 +58,39 @@ In the end you can import the `interface` module. For example:
 const Interface = @import("interface").Interface;
 
 const Repository = Interface(.{
-    .create = fn(anytype, User) anyerror!u32,
-    .findById = fn(anytype, u32) anyerror!?User,
-    .update = fn(anytype, User) anyerror!void,
-    .delete = fn(anytype, u32) anyerror!void,
+    .create = fn(User) anyerror!u32,
+    .findById = fn(u32) anyerror!?User,
+    .update = fn(User) anyerror!void,
+    .delete = fn(u32) anyerror!void,
 }, null);
 ```
 
 ## Usage
 
-1. Define an interface with required method signatures:
+### VTable-Based Runtime Polymorphism
+
+The primary use case for this library is creating type-erased interface objects
+that enable runtime polymorphism. This is ideal for storing different
+implementations in collections, returning interface types from functions, or
+building plugin systems.
+
+**1. Define an interface with required method signatures:**
 
 ```zig
 const Repository = Interface(.{
-    .create = fn(anytype, User) anyerror!u32,
-    .findById = fn(anytype, u32) anyerror!?User,
-    .update = fn(anytype, User) anyerror!void,
-    .delete = fn(anytype, u32) anyerror!void,
+    .create = fn(User) anyerror!u32,
+    .findById = fn(u32) anyerror!?User,
+    .update = fn(User) anyerror!void,
+    .delete = fn(u32) anyerror!void,
 }, null);
 ```
 
-2. Implement the interface methods in your type:
+> Note: `Interface()` generates a type whose function set declared implicitly
+> take an `*anyopaque` self-reference. This saves you from needing to include it
+> in the declaration. However, `anyerror` must be included for any fallible
+> function, but can be omitted if your function cannot return an error.
+
+**2. Implement the interface methods in your type:**
 
 ```zig
 const InMemoryRepository = struct {
@@ -84,43 +106,108 @@ const InMemoryRepository = struct {
         return new_user.id;
     }
 
-    // ... other Repository methods
+    pub fn findById(self: InMemoryRepository, id: u32) !?User {
+        return self.users.get(id);
+    }
+
+    pub fn update(self: *InMemoryRepository, user: User) !void {
+        if (!self.users.contains(user.id)) return error.UserNotFound;
+        try self.users.put(user.id, user);
+    }
+
+    pub fn delete(self: *InMemoryRepository, id: u32) !void {
+        if (!self.users.remove(id)) return error.UserNotFound;
+    }
 };
 ```
 
-3. Verify the implementation at compile time:
+**3. Use the interface for runtime polymorphism:**
 
 ```zig
-// In functions that accept interface implementations:
+// Create different repository implementations
+var in_memory_repo = InMemoryRepository.init(allocator);
+var sql_repo = SqlRepository.init(allocator, db_connection);
+
+// Convert to interface objects
+const repo1 = Repository.from(&in_memory_repo);
+const repo2 = Repository.from(&sql_repo);
+
+// Store in heterogeneous collection
+var repositories = [_]Repository{ repo1, repo2 };
+
+// Use through the interface - runtime polymorphism!
+for (repositories) |repo| {
+    const user = User{ .id = 0, .name = "Alice", .email = "[email protected]" };
+    const id = try repo.vtable.create(repo.ptr, user);
+    const found = try repo.vtable.findById(repo.ptr, id);
+}
+
+// Return interface types from functions
+fn getRepository(use_memory: bool, allocator: Allocator) Repository {
+    if (use_memory) {
+        var repo = InMemoryRepository.init(allocator);
+        return Repository.from(&repo);
+    } else {
+        var repo = SqlRepository.init(allocator);
+        return Repository.from(&repo);
+    }
+}
+```
+
+### Compile-Time Validation (Alternative Approach)
+
+For generic functions where you know the concrete type at compile time, you can
+use the interface for validation without the VTable overhead:
+
+```zig
+// Generic function that accepts any Repository implementation
 fn createUser(repo: anytype, name: []const u8, email: []const u8) !User {
-    comptime Repository.satisfiedBy(@TypeOf(repo));
-    // ... rest of implementation
+    // Validate at compile time that repo implements IRepository
+    comptime Repository.validation.satisfiedBy(@TypeOf(repo.*));
+
+    const user = User{ .id = 0, .name = name, .email = email };
+    const id = try repo.create(user);
+    return User{ .id = id, .name = name, .email = email };
 }
 
-// Or verify directly:
-comptime Repository.satisfiedBy(InMemoryRepository);
+// Works with any concrete implementation - no VTable needed
+var in_memory = InMemoryRepository.init(allocator);
+const user = try createUser(&in_memory, "Alice", "[email protected]");
 ```
 
 ## Interface Embedding
 
-Interfaces can embed other interfaces to combine their requirements:
+Interfaces can embed other interfaces to combine their requirements. The
+generated VTable will include all methods from embedded interfaces:
 
 ```zig
 const Logger = Interface(.{
-    .log = fn(anytype, []const u8) void,
-    .getLogLevel = fn(anytype) u8,
+    .log = fn([]const u8) void,
+    .getLogLevel = fn() u8,
 }, null);
 
 const Metrics = Interface(.{
-    .increment = fn(anytype, []const u8) void,
-    .getValue = fn(anytype, []const u8) u64,
+    .increment = fn([]const u8) void,
+    .getValue = fn([]const u8) u64,
 }, .{ Logger });  // Embeds Logger interface
 
-// Now implements both Metrics and Logger methods
-const MonitoredRepository = Interface(.{
-    .create = fn(anytype, User) anyerror!u32,
-    .findById = fn(anytype, u32) anyerror!?User,
-}, .{ Metrics });
+// Implementation must provide all methods
+const MyMetrics = struct {
+    log_level: u8,
+    counters: std.StringHashMap(u64),
+
+    // Logger methods
+    pub fn log(self: MyMetrics, msg: []const u8) void { ... }
+    pub fn getLogLevel(self: MyMetrics) u8 { return self.log_level; }
+
+    // Metrics methods
+    pub fn increment(self: *MyMetrics, name: []const u8) void { ... }
+    pub fn getValue(self: MyMetrics, name: []const u8) u64 { ... }
+};
+
+// Use it with auto-generated wrappers:
+var my_metrics = MyMetrics{ ... };
+const metrics = Metrics.from(&my_metrics);
 ```
 
 > Note: you can embed arbitrarily many interfaces!
@@ -148,12 +235,12 @@ const BadImpl = struct {
 
 ## Complex Types
 
-The interface checker supports complex types including:
+The interface checker supports complex types including structs, enums, arrays,
+and optionals:
 
 ```zig
-const ComplexTypes = Interface(.{
+const Processor = Interface(.{
     .process = fn(
-        anytype,
         struct { config: Config, points: []const DataPoint },
         enum { ready, processing, error },
         []const struct {
@@ -163,4 +250,52 @@ const ComplexTypes = Interface(.{
         }
     ) anyerror!?ProcessingResult,
 }, null);
+...
+```
+
+## Choosing Between VTable and Compile-Time Approaches
+
+Both approaches work from the same interface definition and can be used
+together:
+
+| Feature             | VTable Runtime Polymorphism                                     | Compile-Time Validation            |
+| ------------------- | --------------------------------------------------------------- | ---------------------------------- |
+| **Use Case**        | Heterogeneous collections, plugin systems, returning interfaces | Generic functions, static dispatch |
+| **Performance**     | Function pointer indirection                                    | Zero overhead (monomorphization)   |
+| **Binary Size**     | Smaller (shared dispatch code)                                  | Larger (per-type instantiation)    |
+| **Flexibility**     | Store in arrays, return from functions                          | Known types at compile time        |
+| **Type Visibility** | Type-erased (`*anyopaque`)                                      | Concrete type always known         |
+| **Method Calls**    | `interface.vtable.method(interface.ptr, args)`                  | Direct: `instance.method(args)`    |
+| **When to Use**     | Need runtime flexibility                                        | Need maximum performance           |
+
+**Example using both:**
+
+```zig
+// Define once
+const Repository = Interface(.{
+    .save = fn(Data) anyerror!void,
+}, null);
+
+// Use compile-time validation for hot paths
+fn processBatch(repo: anytype, items: []const Data) !void {
+    comptime Repository.validation.satisfiedBy(@TypeOf(repo.*));
+    for (items) |item| {
+        try repo.save(item);  // Direct call, can be inlined
+    }
+}
+
+// Use VTable for plugin registry
+const PluginRegistry = struct {
+    repositories: []Repository,
+
+    fn addPlugin(self: *PluginRegistry, repo: Repository) void {
+        self.repositories = self.repositories ++ &[_]Repository{repo};
+    }
+
+    fn saveToAll(self: PluginRegistry, data: Data) !void {
+        for (self.repositories) |repo| {
+            try repo.vtable.save(repo.ptr, data);
+        }
+    }
+};
 ```