How to fetch from cursor over single column of composite type into a variable of that type in PL/pgSQL?

Question

Given:

CREATE TYPE my_struct AS (
    a int4,
    b text,
    c float4
);

DO $$
DECLARE
    my_cursor refcursor;
    my_value my_struct;
BEGIN
    OPEN my_cursor FOR SELECT (1, 'a', 10.0)::my_struct;
    FETCH my_cursor INTO my_value; -- ERROR!
END
$$

Postgres raises an error on FETCH:

ERROR: invalid input syntax for type integer: "(1,a,10)"

Which looks like it's trying to stuff the entire composite value from the cursor into my_value.a field. I also tried

FETCH my_cursor INTO my_value.a, my_value.b, my_value.c;

But it raises the same error. What am I doing wrong and how do I do it correctly? I want to end up with my_value = (1, 'a', 10.0), or my_value IS NULL when the query yields NULL in the column.

Answer 1

Looks like there is simply no straightforward way to do it, but I found a somewhat palatable workaround, by naming the column and going through a temporary record.

DO $$
DECLARE
    my_cursor refcursor;
    my_value my_struct;
    my_record record;
BEGIN
    OPEN my_cursor FOR
    SELECT (1, 'a', 10.0)::my_struct AS the_value;
                
    FETCH my_cursor INTO my_record;
    my_value := my_record.the_value;
    RAISE NOTICE '%', my_value;
END
$$