subtract
Subtract the receiver from the given float, destroying one or the other if it's mutable and canDestroy is true. Because of the requirement that the argument be a float rather than an arbitrary A_Number, this is usually only used for double-dispatching.
Return
The difference, possibly recycling one of the inputs if canDestroy is true.
Parameters
float
The float to subtract the receiver from.
can
Whether a mutable receiver or argument may be destroyed and/or recycled to hold the difference.