Because trilean stores its data in two bits, it is possible for a variable to track its last certain state. In other words, if a trilean is “true” or “false,” and then is set to “maybe”, that true/false value is still being stored behind the scenes.
To make this useful, trilean offers a
certain() function, which returns
the last certain state of the variable without actually modifying itself.
tril foo = true; foo = maybe; bool bar = foo.certain(); // bar is now 'true', while foo is still 'maybe'
This behavior can also be used to revert a trilean to its last certain state.
tril foo = true; foo = maybe; foo = foo.certain(); // foo is now 'true'
The concept of “certainty” technically allows one to recognize and use four trilean states:
Certain true (
if( foo ))
Uncertain true (
if( ~foo && foo.certain() ))
Uncertain false (
if (~foo && !foo.certain() ))
Certain false (
The “magical” behavior of assigning the constant “maybe” not affecting the previous certain state is achieved through “uncertainty” variables. Any time an uncertainty is assigned to a trilean, only the uncertainty of the trilean is affected.
The constant “maybe” is usually the only uncertainty object you will interact
with. However, it is possible to create your own
certainty. Be aware that
this data type does not provide any mechanism for modifying it after creation.
uncertainty my_maybe(true); uncertainty my_certain(false);
As is expected, an uncertainty can never match “true” or “false”, or be
directly cast to a boolean. However, the
~ operator works as with trileans.
if(~my_maybe) // This passes. if(~my_certain) // This fails. if(~my_certain == false) // This passes.
The usefulness of an uncertainty variable is, quite probably, limited to allowing manipulation of a trilean’s certainty.