Open Radar

 
Summary:
Currently, manual memory allocation in native Swift works by calling UnsafeMutablePointer.alloc(capacity) which returns an UnsafeMutablePointer.

In practice, many memory allocators only allocate memory in specific sizes, so the memory we get from UnsafeMutablePointer.alloc(capacity) might actually have a larger capacity than what we asked for. Currently Swift offers no native way to use the actual allocated capacity.

What I'm proposing is that UnsafeMutablePointer offer another method to allocate memory that also returns the actual capacity of the new memory.

For example a potential version could look like this:

extension UnsafeMutablePointer {
    // TODO: find a better name
    static func allocSmart(minimumCapacity: Int) -> (UnsafeMutablePointer<Memory>, Int) {
        // Example implementation using fact that Swift currently uses malloc for memory allocation
        let stride = strideof(Memory)
        let actualCapacity = malloc_good_size(stride * minimumCapacity) / stride
        return (alloc(actualCapacity), actualCapacity)
    }
}

Steps to Reproduce:


Expected Results:


Actual Results:


Version:
Xcode 7.2b4 (7C62b)
Apple Swift version 2.1.1 (swiftlang-700.1.101.13 clang-700.1.81)
OS X 10.11.1 (15B42)