Why does `static foreach` lead to something calling `~=` internally?

[0xEAB]

Why does this `static foreach` lead to hidden usage of operator 
`~=` calls in some cases?

> static foreach(i; 0 .. cnt)

> onlineapp.d(9): Error: cannot use operator ~= in @nogc delegate 
> onlineapp.xv!(myUDA("/")).__funcliteral2.__lambda1




> import std.traits;
> 
> private @safe pure nothrow @nogc
> {
>     enum xv(alias uda) = function()
>     {
>         enum cnt = 10;
> 
>         static foreach(i; 0 .. cnt)
>         {
>         }
>     };
> }
> 
> struct myUDA
> {
>     string path;
> }
> 
> @myUDA("/")
> void doSth(string path)
> {
> }
> 
> extern(C) void main()
> {
>     xv!(getUDAs!(doSth, myUDA))();
> }


Try: https://run.dlang.io/is/clQgeA