Function ExecEvalArrayCoerce

src/backend/executor/execExprInterp.c:2995–3028

* Evaluate an ArrayCoerceExpr expression. * * Source array is in step's result variable. */

 * Source array is in step's result variable.
 */
void
ExecEvalArrayCoerce(ExprState *state, ExprEvalStep *op, ExprContext *econtext)
{
	Datum		arraydatum;

	/* NULL array -> NULL result */
	if (*op->resnull)
		return;

	arraydatum = *op->resvalue;

	/*
	 * If it's binary-compatible, modify the element type in the array header,
	 * but otherwise leave the array as we received it.
	 */
	if (op->d.arraycoerce.elemexprstate == NULL)
	{
		/* Detoast input array if necessary, and copy in any case */
		ArrayType  *array = DatumGetArrayTypePCopy(arraydatum);

		ARR_ELEMTYPE(array) = op->d.arraycoerce.resultelemtype;
		*op->resvalue = PointerGetDatum(array);
		return;
	}

	/*
	 * Use array_map to apply the sub-expression to each array element.
	 */
	*op->resvalue = array_map(arraydatum,
							  op->d.arraycoerce.elemexprstate,
							  econtext,
							  op->d.arraycoerce.resultelemtype,
							  op->d.arraycoerce.amstate);
}

/*
 * Evaluate a ROW() expression.