struct with 2 cells vs std::pair?

Question

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What is the difference between using a struct with two fields and a pair?

Dear all,

I have a little question about pairs and struct. Is there any advantage to use a std::pair instead of a struct with two cells ? I have used pairs for a while but the main problem is readability : If you want to represent for example a duple (int "label", double "value") you can use either a :

typedef std::pair<int,double> myElem;

or a

typedef struct {
    int label;
    double value;
} myElem;

The code becomes more readable if your statements have a "semantic" sense (you will always know what x.label is. that's not the case with x.first).

However, I guess there is an advantage using pair. Is it more performant or something else?

Answer 1

In terms of performance: it's unlikely to change anything, you're just sugar coating it.

In terms of usability, I would rather use a custom struct, which can be declared this way (by the way):

struct MyElement
{
  int label;
  double value;
};

I am a strong proponent of strong typing, and I much prefer a "real" structure (and better yet, class) than an ad-hoc tuple whenever it's more than a fleeting thing.

Mainly because:

• As you noted first and second don't carry much meaning
• You cannot add methods / other fields to a std::pair
• You cannot add class invariants to a std::pair

All in all, I really think that maintenance benefits from using a custom dedicated structure that a one-size-fits-them-all tuple.