imploding/using arrays for IN (...)

Passing an array to a PL/pgSQL function, is it
possible to implode it and use with IN (...) ? For
example:

my_func(int[])
 ids := implode_func($1);

 select *
 from x
 where id in (ids);


I tried concatenating ids together with ',', but the
query gives an integer/text cast error. Or, is it
possible use arrays in IN()?

 select *
 from x
 where id in ({1,2,3});


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