DM-9938: Make some afw types hashable #17
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TallJimbo
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Nov 1, 2018
| return 179; | ||
| } else { | ||
| return utils::hashCombine(17, _minimum, _maximum); | ||
| } |
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I suspect the magic numbers here are completely arbitrary and just need to be nonzero and deterministic, but even if that's the case I think a code comment would be welcome. That's especially true if they have other useful properties, like being odd numbers.
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I feel better if they're prime numbers (though I do violate that rule with 42 😉), but yes, they're basically arbitrary. I'll go ahead and add a comment, but I feel like there's too much boilerplate already.
P.S. Actually, the seed need not be deterministic, as long as you only generate it once -- that's how you get salted hashes.
Point and Extent are the only subclasses of CoordinateBase that are equality-comparable, so they're the only ones that should be hashable, but this means duplicating the actual hash algorithm between the two classes. I've also added support for std::hash and unit tests of hash's behavior.
The affected types are Angle, Box2D, Box2I, and SpherePoint.
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This PR switches
Point's existing hash to usestd::hash, and adds hash support to all value types ingeom(defined as supportingoperator==).This PR requires lsst/utils#65.