Is Using `std::tie` for Comparison Operators in Structs a Sound Approach?

Using 'tuple' and 'tie' for comparison operators: Is it a sound approach?

When dealing with small structs with only two members, the choice between using a standard pair or a tuple can be a dilemma. While pairs offer convenient operators such as operator< for strict-weak-ordering, their variable names can be less than intuitive. Tuples, on the other hand, provide flexibility but can lead to less clear code.

To address these drawbacks, some have suggested relying solely on tuple operations to implement comparison operators. This can greatly simplify the process, as seen in the code snippet below:

bool operator<(MyStruct const& lhs, MyStruct const& rhs) {
  return std::tie(lhs.one_member, lhs.another, lhs.yet_more) <
         std::tie(rhs.one_member, rhs.another, rhs.yet_more);
}

However, there are potential drawbacks to consider:

• Possible performance concerns: While the tuple-based approach simplifies implementation, it may not be as efficient as custom operators tailored to the specific struct data structure. If performance is a critical consideration, profiling the comparison operation may be advisable.
• Presentation limitations: Using tie() requires all members to be included in the comparison, which may not always be desirable. For example, if only certain members are relevant for ordering, the custom operator allows for selective comparison.
• Code readability: The tuple-based code can become cluttered as the number of members increases or the data structure becomes more complex.

Ultimately, the choice of using tuple and tie for comparison operators depends on the specific needs of the application. If ease of implementation and maintainability are prioritized, the tuple-based approach may be a suitable option. However, if performance optimizations or custom comparison criteria are essential, a bespoke operator implementation might be more appropriate.

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