Any plans to add a license?

First of all, thanks for the effort. I tried this library with zig v0.9.1 and I got started very fast.

However, one thing that would be nice is to use zig-ecs with the current v0.11.0 version of the zig compiler.
Currently, if I try to build a simple project (or the examples) using zig v0.11.0-dev.1571+c1f71963a I receive a quite generic error:

$ zig build
error: zigecs-test...
error: The following command terminated unexpectedly:
/home/stefanpartheym/.zvm/master/zig build-exe /home/stefanpartheym/develop/stefanpartheym/zigecs-test/src/main.zig --cache-dir /home/stefanpartheym/develop/stefanpartheym/zigecs-test/zig-cache --global-cache-dir /home/stefanpartheym/.cache/zig --name zigecs-test --pkg-begin ecs /home/stefanpartheym/develop/stefanpartheym/zigecs-test/deps/zig-ecs/src/ecs.zig --pkg-end --enable-cache 
error: the following build command failed with exit code 11:
/home/stefanpartheym/develop/stefanpartheym/zigecs-test/zig-cache/o/ee157244c8abf2f8e61ae7f5813ecc82/build /home/stefanpartheym/.zvm/master/zig /home/stefanpartheym/develop/stefanpartheym/zigecs-test /home/stefanpartheym/develop/stefanpartheym/zigecs-test/zig-cache /home/stefanpartheym/.cache/zig run

If I then try to execute the actual command line run by zig build:

$ /home/stefanpartheym/.zvm/master/zig build-exe /home/stefanpartheym/develop/stefanpartheym/zigecs-test/src/main.zig --cache-dir /home/stefanpartheym/develop/stefanpartheym/zigecs-test/zig-cache --global-cache-dir /home/stefanpartheym/.cache/zig --name zigecs-test --pkg-begin ecs /home/stefanpartheym/develop/stefanpartheym/zigecs-test/deps/zig-ecs/src/ecs.zig --pkg-end --enable-cache
fish: Job 1, '/home/stefanpartheym/.zvm/maste…' terminated by signal SIGSEGV (Adressbereichsfehler)

... the process segfaults.

I suspect, this is may be due to some very complex comptime syntax in src/ecs/component_storage.zig, which might be deprecated in current compiler versions:
In line 186 of component_storage.zig there is pub usingnamespace if (is_empty_struct). Which, if I remove like follows, reveals a different error (but at least not a segfault):

diff --git a/src/ecs/component_storage.zig b/src/ecs/component_storage.zig
index e3aa6b7..72a4408 100644
--- a/src/ecs/component_storage.zig
+++ b/src/ecs/component_storage.zig
@@ -183,17 +183,6 @@ pub fn ComponentStorage(comptime Component: type, comptime Entity: type) type {
             return self.set.len();
         }
 
-        pub usingnamespace if (is_empty_struct)
-            struct {
-                /// Sort Entities according to the given comparison function. Only T == Entity is allowed. The constraint param only exists for
-                /// parity with non-empty Components
-                pub fn sort(self: Self, comptime T: type, context: anytype, comptime lessThan: fn (@TypeOf(context), T, T) bool) void {
-                    std.debug.assert(T == Entity);
-                    self.set.sort(context, lessThan);
-                }
-            }
-        else
-            struct {
                 /// Direct access to the array of objects
                 pub fn raw(self: Self) []Component {
                     return self.instances.items;
@@ -262,7 +251,6 @@ pub fn ComponentStorage(comptime Component: type, comptime Entity: type) type {
                         self.set.arrange(length, swap_context, SortContext.sort, swap_context);
                     }
                 }
-            };
 
         /// Direct access to the array of entities
         pub fn data(self: Self) []const Entity {

Using this patch will result in the following compilation error:

deps/zig-ecs/src/ecs/registry.zig:287:13: error: unable to resolve comptime value
        self.assure(@TypeOf(value)).add(entity, value);
        ~~~~^~~~~~~
deps/zig-ecs/src/ecs/registry.zig:287:13: note: argument to function being called at comptime must be comptime-known
deps/zig-ecs/src/ecs/registry.zig:217:54: note: expression is evaluated at comptime because the generic function was instantiated with a comptime-only return type
    pub fn assure(self: *Registry, comptime T: type) *Storage(T) {
                                                     ^~~~~~~~~~~
referenced by:
    add__anon_4436: deps/zig-ecs/src/ecs/registry.zig:287:13
    main: src/main.zig:16:8
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

Finally, as reference, the build.zig and src/main.zig files I used:

build.zig:

const std = @import("std");

pub fn build(b: *std.Build) void {
    const target = b.standardTargetOptions(.{});
    const optimize = b.standardOptimizeOption(.{});

    const exe = b.addExecutable(.{
        .name = "zigecs-test",
        .root_source_file = .{ .path = "src/main.zig" },
        .target = target,
        .optimize = optimize,
    });
    exe.addModule("ecs", b.createModule(.{
        .source_file = std.build.FileSource{ .path = "deps/zig-ecs/src/ecs.zig" },
    }));
    exe.install();

    const run_cmd = exe.run();
    run_cmd.step.dependOn(b.getInstallStep());
    if (b.args) |args| {
        run_cmd.addArgs(args);
    }

    const run_step = b.step("run", "Run the app");
    run_step.dependOn(&run_cmd.step);

    const exe_tests = b.addTest(.{
        .root_source_file = .{ .path = "src/main.zig" },
        .target = target,
        .optimize = optimize,
    });

    const test_step = b.step("test", "Run unit tests");
    test_step.dependOn(&exe_tests.step);
}

src/main.zig

const std = @import("std");
const builtin = @import("builtin");
const ecs = @import("ecs");

const Position = struct {
    x: f32,
    y: f32,
};

pub fn main() !void {
    std.debug.print("## Testing zig-ecs (zig v{}) ##\n", .{ builtin.zig_version });

    var reg = ecs.Registry.init(std.heap.page_allocator);

    var player = reg.create();
    reg.add(player, Position{ .x = 10, .y = 10 });
}

Thanks and best regards
Stefan

Steps to reproduce

Run the view_vs_groups.zig example but comment the createEntities(&reg) function
https://raw.githubusercontent.com/prime31/zig-ecs/master/examples/view_vs_group.zig

Expected

Program to run as normal. There won't be anything to iterate, but that shouldn't crash the program.

Actual

panic: cast causes pointer to be null

I don't get it, why doesn't it work 🤔

Code:

...
{
    var group = world.group(.{ Position, Orbiting }, .{}, .{});
    var group_iter = group.iterator(struct { pos: *Position, orb: *Orbiting });

    while (group_iter.next()) |e| {
        ...
    }
}

{
    var group = world.group(.{ Position, Renderer }, .{}, .{});
    var group_iter = group.iterator(struct { pos: *Position, ren: *Renderer });

    while (group_iter.next()) |e| {
        ...
    }
}
...

Error Logs:

thread 258336 panic: reached unreachable code
/nix/store/ypzkr8d6sff2vcdjadcbblqdwjf1ia72-zig-0.12.0-dev.1+a327d8b99/lib/std/debug.zig:343:14: 0x342e6c in assert (z-space)
    if (!ok) unreachable; // assertion failure
             ^
/home/jp3/.local/src/z-space/libs/zig-ecs/src/ecs/registry.zig:530:33: 0x344d73 in group__anon_6485 (z-space)
                std.debug.assert(check);
                                ^
/home/jp3/.local/src/z-space/src/main.zig:74:36: 0x3424b4 in main (z-space)
            var group = world.group(.{ Position, Renderer }, .{}, .{});
                                   ^
/nix/store/ypzkr8d6sff2vcdjadcbblqdwjf1ia72-zig-0.12.0-dev.1+a327d8b99/lib/std/start.zig:564:22: 0x341dc9 in main (z-space)
            root.main();
                     ^
???:?:?: 0x7ffff7d1facd in ??? (libc.so.6)
Unwind information for `libc.so.6:0x7ffff7d1facd` was not available, trace may be incomplete

PS. Did you thought about adding better error messages - it would have been really helpful 😄

Problem

Not able to create an Owning Group with no includes and no exludes.

pub const Position = struct { x: f32, y: f32 };

pub fn main() !void {
    var reg = ecs.Registry.init(std.heap.c_allocator);
    defer reg.deinit();

    var e = reg.create();
    reg.add(e, Position { .x = 1, .y = 1 });

    var group = reg.group(.{Position }, .{}, .{});   // <-----
}

Result

fails assert in registry.zig: 471
std.debug.assert(owned.len + includes.len + excludes.len > 1);

Am I using the library incorrectly?

Hi, I know that Zig can compile using the C ABI, and I'd like try binding this to Odin. Would there be any difficulties when using this as a static/dynamic library?

The Readme states that...

The same example using a non-owning Group:

var group = reg.group(.{}, .{ Velocity, Position }, .{});
group.each(each);

fn each(e: struct { vel: *Velocity, pos: *Position }) void {
    e.pos.*.x += e.vel.x;
    e.pos.*.y += e.vel.y;
}

zig complains:

error: no member named 'each' in struct '.zig-ecs.ecs.groups.BasicGroup'

After looking for it I only managed to find the method each for OwningGroups.
Not that I know if there should or shouldn't be such method but just wanted to point out that the readme seems(?) wrong.