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Auto Variable Assigning Array Does Not Copy

Started by TrevorThoele Feb 20, 2021 at 12:59 AM 3 replies 4.6k views

Original Post

Feb 20, 2021 at 12:59 AM

Declaring a variable as auto and assigning it to an array will not perform a shallow copy, instead effectively reusing the underlying references such that modifying one of the two arrays will modify the other. Declaring the variable as the array type explicitly will result in a copy. Is this something that's known/a feature?

Consider the two fragments below:

array<int> input = {1, 2, 3};
auto copied = input;
copied.insertLast(4);
// copied.length() == 4

array<int> input = {1, 2, 3};
const auto copied = input;
input.insertLast(4);
// copied.length() == 4

WitchLord

Mod

1,118

WitchLord

Feb 20, 2021 at 7:32 PM

Yes, this is known and documented.

http://www.angelcode.com/angelscript/sdk/docs/manual/doc_datatypes_auto.html

The auto type will prefer handles where it can, to avoid making copies.

If you want the copy to be made, either declare the variable with the real type, or make an explicit copy.

TrevorThoele

Author

TrevorThoele

Feb 20, 2021 at 10:17 PM

@WitchLord Ah, ok. I did not consider that the array would be considered an array. From what I understand, arrays are reference types. Is it correct to treat all reference types as handles when using them?

WitchLord

Mod

1,118

WitchLord

Feb 21, 2021 at 6:57 PM

As a general rule you should prefer to use handles when working with reference types to avoid unnecessary memory copies and improve performance. But there is obviously nothing wrong to making a copy when you actually need to preserve the original while modifying the copy.

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