CODEWITHSUNDEEP
swiftunsafe-pointers
jeudesprits
jeudesprits

Reputation: 45

Is it possible to get from Any type his UnsafeRawPointer and length?

I just want call C function

static  inline  uint64_t  wyhash(const void* key,  uint64_t  len, uint64_t  seed)

from Swift like that 

func hash<T: Any>(key: T, seed: UInt64) -> UInt64 { wyhash(...) }

Is it possible? And how?

Upvotes: 0

Views: 250

Answers (1)

Rob Napier
Rob Napier

Reputation: 299355

To compute the size, use MemoryLayout:

func hash<T>(key: T, seed: UInt64) -> UInt64 {
    let len = UInt64(MemoryLayout.size(ofValue: key))
    return withUnsafePointer(to: key) { myhash($0, len, seed) }
}

Keep in mind that structural types may have internal padding, and I don't believe Swift promises that to be initialized. So you may wind up hashing random values if you're not careful what you pass here. And of course types may have non-obvious internal state that can cause "equal" values to hash differently or vice versa. Given the likelihood of difficult-to-diagnose bugs, I would typically suggest writing specific overloads for types you know are acceptable to this function rather than trying to hash over Any. At a minimum, I'd constrain T to some protocol (with no syntactic requirements) that expresses "I've checked that this type is myhash-able."

Upvotes: 1

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