Cast arrays in Apex

Question

Its been a long time since I casted an array and cant remember if it can be done the way Im hoping.

I have an array of type Row (Row[] rows) that is returned from a method. The method I need to pass it into takes DataRow[] dataRows. DataRows is a child of Row.

I am trying to cast like (DataRow[]) rows when I pass in the param, but its no working.

CODE:

Row[] rows = getRows();
savetable(id, (DataRow[]) rows);

Obviously its not working for me, but is there a way to cast arrays in some similar manner?

The inheritence structure is basic:

class Row()
{
    (variables/methods)
}

class DataRow extends Row()
{
    (variables/methods)
}

Are these custom types? Can you share the actual inheritance structure? — Adrian Larson, Jun 01 '17 at 21:17

sfdcfox · Accepted Answer · 2017-06-01T21:32:48.290

Sadly, this doesn't work, because collection inheritance is broken. As I outlined in my previous answer, the following code demonstrates the inheritance problem:

class c1 {

}
class c2 extends c1 {

}
// All C2s are C1s, but this won't compile
Map<String, c2> m1 = new Map<String, c1>();
// Not all C2s are C1s, but this compiles and can crash.
Map<String, c1> m2 = new Map<String, c2>();

Instead, you have to create a list, and copy the elements individually:

DataRows[] datarows = new DataRows[0];
for(Row row: getRows()) {
    datarows.add(row);
}
savetable(id, datarows);

I still plan on bringing this up with the Apex PM when I get a moment. Maybe someday this will work as intended.

gNerb · Answer 2 · 2017-06-01T21:55:21.797

-1

You can only use type casting when you are using related objects (virtual classes/inheritance)

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_casting.htm

In general, all type information is available at runtime. This means that Apex enables casting, that is, a data type of one class can be assigned to a data type of another class, but only if one class is a child of the other class. Use casting when you want to convert an object from one data type to another.

Basically, if dataRow is not a child/parent of Row, you can't type cast it.

You'll have to manually define this behavior.

public static DataRow[] convertFromRows(Row[] rows) {
    DataRow[] result = new DataRow[];

    for (Row r : rows) {
        DataRow tmp = new DataRow();
        // Work your magic here
        result.add(tmp);
    }

    return result;
}

Finally:

saveTable(id, DataRow.convertFromRows(rows));

edited Jun 01 '17 at 21:55

answered Jun 01 '17 at 21:22

gNerb

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You can't type-cast it anyways, because collection casting is broken. – sfdcfox Jun 01 '17 at 21:28
Yea, I read your answer. I just did some testing though and it seems its only broken in 1 direction. I can typecast a child to the parent class but I cannot typecast a parent to a child class with collections. – gNerb Jun 01 '17 at 21:36
It's broken both directions, because it allows you to type-cast a smaller collection into a larger collection, thus resulting in runtime errors. – sfdcfox Jun 01 '17 at 21:37
I'm not sure I understand then, I was able to get it to work without runtime errors using a few simple classes. – gNerb Jun 01 '17 at 21:39
Object[] a = new String[0]; a.add(5); – sfdcfox Jun 01 '17 at 21:41
`class c1 {
} class c2 extends c1 {

} c1[] cc = new c2[0]; cc.add(new c1());`
– sfdcfox Jun 01 '17 at 21:43

Cast arrays in Apex

2 Answers2