BufferWithManagedBuffer.swift

public struct Buffer<T> : Collection {
    private var _buf: ManagedBuffer<Int, T>
    
    public init(capacity: Int) {
        precondition(!(T.self is AnyObject.Type))
        _buf = ManagedBuffer.create(minimumCapacity: capacity) { _ in capacity }
    }
    
    public var count: Int {
        return _buf.withUnsafeMutablePointerToHeader { $0.pointee }
    }
    
    public var startIndex: Int { return 0 }
    public var endIndex: Int { return count }
    
    public func index(after index: Int) -> Int {
        return index + 1
    }
    
    public subscript(index: Int) -> T {
        get { return _buf.withUnsafeMutablePointerToElements { $0[index] } }
        set { _buf.withUnsafeMutablePointerToElements { $0[index] = newValue } }
    }
}