Support mixed operators with other strong typedefs and noncommutative mixed operators #75
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gerboengels
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Mixed operators, such as mixed_addition, work fine when the underlying type and the other type are compatible. But when the other type is a strong_typedef, and they are not convertible (which is the whole point of using a strong_typedef), mixed operators do not work. This commit checks whether the other type is a strong typedef, and if so, applies the operator on the underlying type, instead of the strong typedef itself. Two use cases: - Mixing a strong typedef for some value (such as 'year', like 2018) and some offset related to such values (such as 'year_offset', like +3). These types should not be implicitly convertible, but you do want 'year' to support mixed addition with 'year_offset' on the underlying (int) type. - Mixing an amount (euro's) strong typedef with a percentage strong typedef. These types are obviously not convertible, but mixed_multiplication<amount, percentage> on the underlying doubles is desirable
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Subtraction and division are noncommutative ((a - b) != (b - a)), and when mixing
different types you might not want these operators to work both ways.
This commit adds mixed_[operator]_noncommutative, which does _not_ declare the
operator overloads with the strong_typedef as the right hand side and the
other (mixed) type as the left hand side
Example:
struct year : strong_typedef<year, int>,
mixed_subtraction_noncommutative<year, int> {};
year y(2018);
y - 3; // OK
3 - y; // compile error, operator not found.
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Github accepted a review I did even though there had been a forced push which fixed what I wanted to point out. I only just realized that I could cancel the review. This addition looks good to me, and I'll certainly use it when defining quantity types. |
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I agree, thank's for doing that. |
saraedum
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The first commit enables 'mixed' operators with other strong_typedefs, by applying the operator on the underlying type of both strong_typedefs.
The second commits adds noncommutative mixed operators, useful for subtraction and division.
Use case demonstrating both cases: