Populating NSRectPointer in Swift

I'm translating some Objective-C code I got from a book to Swift. The code in question is a custom implementation of an NSTextContainer method:

-(NSRect)lineFragmentRectForProposedRect:(NSRect)proposedRect
                          sweepDirection:(NSLineSweepDirection)sweepDirection
                       movementDirection:(NSLineMovementDirection)movementDirection
                           remainingRect:(NSRectPointer)remainingRect
{

 // ... now set value of the struct pointed at by NSRectPointer
 *remainingRect = NSRectMake(0, 0, 100, 50);

 //...
 return mainRect;
}

I struggling to replicate this in Swift - no matter what I try I keep getting told that I can't assign to a let variable.

NSRectPointer is defined as

public typealias NSRectPointer = UnsafeMutablePointer<NSRect>

and UnsafeMutablePointer has a

/// Access the underlying raw memory, getting and setting values.
public var memory: Memory { get nonmutating set }

property, therefore the Swift equivalent of the Objective-C code

*remainingRect = NSRectMake(0, 0, 100, 50);

should be

remainingRect.memory = NSMakeRect(0, 0, 100, 50)