Pavel Stehule <pavel.stehule@gmail.com> writes:
> with get_fn_expr_arg_stable() we are able to fix second parameter
> without some performance issues.
No, that will create its own performance issues ---
get_fn_expr_arg_stable isn't especially cheap.
If there were a really strong reason why we had to do it,
then I'd agree, but frankly the argument for disallowing
a variable delimiter is too thin.
regards, tom lane