Function do_cast_value

src/pl/plpgsql/src/pl_exec.c:7671–7703

---------- * do_cast_value Slow path for exec_cast_value. * ---------- */

 * ----------
 */
static Datum
do_cast_value(PLpgSQL_execstate *estate,
			  Datum value, bool *isnull,
			  Oid valtype, int32 valtypmod,
			  Oid reqtype, int32 reqtypmod)
{
	plpgsql_CastHashEntry *cast_entry;

	cast_entry = get_cast_hashentry(estate,
									valtype, valtypmod,
									reqtype, reqtypmod);
	if (cast_entry)
	{
		ExprContext *econtext = estate->eval_econtext;
		MemoryContext oldcontext;

		oldcontext = MemoryContextSwitchTo(get_eval_mcontext(estate));

		econtext->caseValue_datum = value;
		econtext->caseValue_isNull = *isnull;

		cast_entry->cast_in_use = true;

		value = ExecEvalExpr(cast_entry->cast_exprstate, econtext,
							 isnull);

		cast_entry->cast_in_use = false;

		MemoryContextSwitchTo(oldcontext);
	}

	return value;
}

/* ----------
 * get_cast_hashentry			Look up how to perform a type cast