Type alias for Zig bindings

alias.zig

fn Alias(a: type, b: type) type {
  return struct {
    fn fixType(t: anytype) void {
      var info = @typeInfo(t.*);
      switch(info) {
        .Pointer => |*ptr| {
          if(ptr.child == a) {
            ptr.child = b;
            ptr.alignment = @alignOf(a);
          }
        },
        else => {},
      }
      t.* = @Type(info);
    }

    fn FuncType(fptr: anytype) type {
      var ptr_type = @typeInfo(@TypeOf(fptr));
      var child_type = @typeInfo(ptr_type.Pointer.child);
      var fn_type = &child_type.Fn;
      fixType(&fn_type.return_type.?);

      var params: [fn_type.params.len]std.builtin.Type.Fn.Param = undefined;
      @memcpy(&params, fn_type.params);
      for(params[0..]) |*param|
        fixType(&param.type.?);
      fn_type.params = params[0..];

      ptr_type.Pointer.child = @Type(child_type);
      return @Type(ptr_type);
    }

    pub fn cast(func: anytype) FuncType(&func) {
      return @ptrCast(&func);
    }
  };
}

// Usage
pub const Foo = struct {
  const alias = Alias(c.foo_t, Foo);
  pub const init = alias.cast(c.foo_init);
  pub const func = alias.cast(c.foo_func);
};

var foo = Foo.init();
// foo.func() impossible as of Zig 0.13 because of https://github.com/ziglang/zig/issues/18233
Foo.func(foo);