Allow specifying pairs in Entity get/set functions

src/entity.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 const Allocator = std.mem.Allocator;
 
+const meta = @import("./meta.zig");
 const flecs = @import("./main.zig");
 const Path = flecs.Path;
 const c = flecs.c;
@@ -84,10 +85,10 @@ pub fn Entity(comptime ctx: anytype) type {
         /// To set their values you'll need to use `set(...)` on the
         /// `Entity` returned from this function.
         pub fn init(world: *World, config: Config, ids: anytype) !Self {
-            const meta = @typeInfo(@TypeOf(ids));
+            const info = @typeInfo(@TypeOf(ids));
-            if (meta != .Struct or (meta.Struct.is_tuple == false and meta.Struct.fields.len > 0))
+            if (info != .Struct or (info.Struct.is_tuple == false and info.Struct.fields.len > 0))
                 @compileError("Expected tuple or empty struct, got '" ++ @typeName(@TypeOf(ids)) ++ "'");
-            if (meta.Struct.fields.len > c.FLECS_ID_DESC_MAX)
+            if (info.Struct.fields.len > c.FLECS_ID_DESC_MAX)
                 @compileError("Adding more than FLECS_ID_DESC_MAX ids");
 
             var id = if (config.id) |i| i.raw else null;
@@ -303,7 +304,7 @@ pub fn Entity(comptime ctx: anytype) type {
 
         /// Gets a value copy of a component.
         /// If the component does not exist, returns null.
-        pub fn get(self: Self, comptime T: type) ?T {
+        pub fn get(self: Self, comptime T: anytype) ?meta.AnyToType(T) {
             return if (getRef(self, T)) |p| p.* else null;
         }
 
@@ -313,8 +314,8 @@ pub fn Entity(comptime ctx: anytype) type {
         /// The returned pointer may become invalid after calling other Flecs
         /// functions, notably when an `Entity` moves to another table caused
         /// by adding or removing other components.
-        pub fn getRef(self: Self, comptime T: type) ?*const T {
+        pub fn getRef(self: Self, comptime T: anytype) ?*const meta.AnyToType(T) {
-            const id = Context.lookup(T).*;
+            const id = Context.anyToId(T);
             const ptr = c.ecs_get_id(self.world.raw, self.raw, id);
             return @alignCast(@ptrCast(ptr));
         }
@@ -329,15 +330,15 @@ pub fn Entity(comptime ctx: anytype) type {
         /// If `getMut` is called when the world is in deferred / readonly
         /// mode, and the component does not yet exist, it will return a
         /// pointer to a temp storage.
-        pub fn getMut(self: Self, comptime T: type) *T {
+        pub fn getMut(self: Self, comptime T: anytype) *meta.AnyToType(T) {
-            const id = Context.lookup(T).*;
+            const id = Context.anyToId(T);
             const ptr = c.ecs_get_mut_id(self.world.raw, self.raw, id);
             return @alignCast(@ptrCast(ptr));
         }
 
-        pub fn set(self: Self, comptime T: type, value: T) void {
+        pub fn set(self: Self, comptime T: anytype, value: meta.AnyToType(T)) void {
-            const id = Context.lookup(T).*;
+            const id = Context.anyToId(T);
-            _ = c.ecs_set_id(self.world.raw, self.raw, id, @sizeOf(T), &value);
+            _ = c.ecs_set_id(self.world.raw, self.raw, id, @sizeOf(@TypeOf(value)), &value);
         }
     };
 }

src/meta.zig

@@ -48,6 +48,34 @@ pub fn isZigString(comptime T: type) bool {
     };
 }
 
+/// Returns the type of the specified expression, which must be either
+/// just a `type`, or a tuple in the form of `.{ TRelation, TTarget }`,
+/// representing a relationship pair in Flecs.
+///
+/// If the expression is a pair, the type is determined like this:
+/// - If `TRelation` is a non-zero-sized type, it is returned.
+/// - If `TTarget` is a non-zero-sized type, it is returned.
+/// - Otherwise, a compile error is raised.
+pub fn AnyToType(comptime expr: anytype) type {
+    switch (@typeInfo(@TypeOf(expr))) {
+        .Type => return expr,
+        .Struct => |s| {
+            if (!s.is_tuple or s.fields.len != 2)
+                @compileError("Expression must be a type or a tuple of two types");
+
+            const TRelation = expr[0];
+            const TTarget = expr[1];
+            if (@TypeOf(TRelation) != type) @compileError("TRelation must be a type, but is " ++ @typeName(@TypeOf(TRelation)));
+            if (@TypeOf(TTarget) != type) @compileError("TTarget must be a type, but is " ++ @typeName(@TypeOf(TTarget)));
+
+            if (@sizeOf(TRelation) > 0) return TRelation;
+            if (@sizeOf(TTarget) > 0) return TTarget;
+            @compileError("Either TRelation or TTarget must be a non-zero-sized type");
+        },
+        else => @compileError("Expression must be a type or a tuple of two types"),
+    }
+}
+
 /// Gets the simplified type name of the specified type.
 /// That is, without any namespace qualifiers.
 pub fn simpleTypeName(comptime T: type) [:0]const u8 {