UInt64 cannot be negative

[frogcjn]

In ImageCache.swift

                let bytesToPurge = self.currentMemoryUsage - self.preferredMemoryUsageAfterPurge

This sentence may EXC_BREAKPOINT, because self.currentMemoryUsage may less then self.preferredMemoryUsageAfterPurge.

and bytesToPruge is UInt64 type inference by Swift.

[cnoon]

Thanks for reporting @frogcjn!

I would say that if you end up seeing this error, then you have set up the memoryCapacity and the preferredMemoryUsageAfterPurge parameters incorrectly. To help guard against this moving forward, I've added a precondition to the ImageCache initializer in 0095691 to prevent you from accidentally making this mistake.

Thanks again. 🍻