Conversion vs subscript operator overload for class wrapping an array

Question

I have a class wrapping an array and want to provide the typical subscript access to its users.

...
class C;
C c;
auto x = c[0];
...

I may both provide conversion

class C
{
    int i[10];
public:
    operator int*() { return i; }
};

and provide subscript operator overload

class C
{
    int i[10];
public:    
    int& operator[](unsigned idx) {
        // eventual out-of-bounds check
        return i[idx]; 
    }
};

Apart from OOB check, which one should be preferred?

Prefer operator[]. See this related question for reasons why. — Evg
– Evg, Commented Nov 28, 2019 at 10:47
Apart from OOB check OOB = out-of-bounds? Range check (maybe, in debug only like in common std::vector::operator[] implementations) alone is worth to prefer the latter. ;-) — Scheff's Cat
– Scheff's Cat, Commented Nov 28, 2019 at 10:52

songyuanyao · Accepted Answer · 2019-11-28 10:53:48Z

3

If you just want to call operator[] on the class C, then just overload operator[]. Don't allow implicit conversion if not necessary. If you provide operator int*, something meaningless and dangerous will be allowed too. e.g.

C c;
if (c) ...;
delete c;

edited Nov 28, 2019 at 10:53

answered Nov 28, 2019 at 10:48

songyuanyao

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2 Comments

Scheff's Cat Over a year ago

Don't allow implicit conversion if not necessary. I just remembered how often I add explicit to constructors to satisfy my paranoidity, and spent +1. ;-)

songyuanyao Over a year ago

@Scheff It's worthwhile, definitely. :)

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