This is attribute gives an estimate of
the number of entries that will be stored in the
KeyMap. It is used to tune the internal properties of the
KeyMap for speed and efficiency. A larger value will result in faster access at the expense of increased
memory requirements. However if the SizeGuess value is much larger than the actual size of the
KeyMap, then there will be little, if any, speed gained by making the SizeGuess even larger. The
default value is 300.
The value of this attribute can only be changed if the KeyMap is empty. Its value can be set
conveniently when creating the KeyMap. An error will be reported if an attempt is made to set or clear
the attribute when the KeyMap contains any entries.