tristate Class Reference

#include <tristate.h>

Public Member Functions
	tristate ()
	tristate (bool boolValue)
	tristate (char c)
	tristate (int intValue)
bool	operator! () const
bool	operator~ () const
tristate &	operator= (const tristate &tsValue)
TQString	toString () const

Friends
bool	operator== (bool boolValue, tristate tsValue)
bool	operator== (tristate tsValue, bool boolValue)
bool	operator!= (bool boolValue, tristate tsValue)
bool	operator!= (tristate tsValue, bool boolValue)

Detailed Description

3-state logical type with three values: true, false and cancelled and convenient operators.

cancelled state can be also called dontKnow, it behaves as null in SQL. A main goal of this class is to improve readibility when there's a need for storing third, cancelled, state, especially in case C++ exceptions are not in use. With it, developer can forget about declaring a specific enum type having just three values: true, false, cancelled.

Objects of this class can be used with similar convenience as standard bool type:

• use as return value when 'cancelled'

  tristate doSomething();

• convert from bool (1) or to bool (2)

  tristate t = true; //(1)
  setVisible(t);   //(2)

• clear comparisons

  tristate t = doSomething();
  if (t) doSomethingIfTrue();
  if (!t) doSomethingIfFalse();
  if (~t) doSomethingIfCancelled();

"! ~" can be used as "not cancelled".

With tristate class, developer can also forget about it's additional meaning and treat it just as a bool, if the third state is irrelevant to the current situation.

Other use for tristate class could be to allow cancellation within a callback function or a TQt slot. Example:

public slots:
  void validateData(tristate& result);

Having the single parameter, signals and slots have still simple look. Developers can alter their code (by replacing 'bool& result' with 'tristate& result') in case when a possibility of canceling of, say, data provessing needs to be implemented. Let's say validateData() function uses a TQDialog to get some validation from a user. While TQDialog::Rejected is returned after cancellation of the validation process, the information about cancellation needs to be transferred up to a higher level of the program. Storing values of type TQDialog::DialogCode there could be found as unreadable, and casting these to int is not typesafe. With tristate class it's easier to make it obvious that cancellation should be taken into account.

Author

Jaroslaw Staniek

Definition at line 99 of file tristate.h.

Constructor & Destructor Documentation

tristate() [1/4]

tristate::tristate ( )

inline

Default constructor, object has cancelled value set.

Definition at line 105 of file tristate.h.

tristate() [2/4]

tristate::tristate ( bool  boolValue )

inline

Constructor accepting a boolean value.

Definition at line 113 of file tristate.h.

tristate() [3/4]

tristate::tristate ( char  c )

inline

Constructor accepting a char value.

It is converted in the following way:

• 2 -> cancelled
• 1 -> true
• other -> false

Definition at line 125 of file tristate.h.

tristate() [4/4]

tristate::tristate ( int  intValue )

inline

Constructor accepting an integer value.

It is converted in the following way:

• 2 -> cancelled
• 1 -> true
• other -> false

Definition at line 136 of file tristate.h.

Member Function Documentation

operator!()

bool tristate::operator! ( ) const

inline

Casting to bool type with negation: true is only returned if the original tristate value is equal to false.

Definition at line 145 of file tristate.h.

operator=()

tristate & tristate::operator= ( const tristate &  tsValue )

inline

Definition at line 153 of file tristate.h.

operator~()

bool tristate::operator~ ( ) const

inline

Special casting to bool type: true is only returned if the original tristate value is equal to cancelled.

Definition at line 151 of file tristate.h.

toString()

TQString tristate::toString ( ) const

inline

Returns

text representation of the value: "true", "false" or "cancelled".

Definition at line 166 of file tristate.h.

Friends And Related Symbol Documentation

operator!= [1/2]

bool operator!= ( bool  boolValue, tristate  tsValue  )

friend

Inequality operator comparing a bool value boolValue and a tristate value tsValue.

Returns

false if both boolValue and tsValue are true or if both boolValue and tsValue are false. Else, returns true.

Definition at line 196 of file tristate.h.

operator!= [2/2]

bool operator!= ( tristate  tsValue, bool  boolValue  )

friend

Inequality operator comparing a tristate value tsValue and a bool value boolValue.

See also

bool operator!=(bool boolValue, tristate tsValue)

Definition at line 206 of file tristate.h.

operator== [1/2]

bool operator== ( bool  boolValue, tristate  tsValue  )

friend

Equality operator comparing a bool value boolValue and a tristate value tsValue.

Returns

true if both

• both tsValue value and boolValue are true, or
• both tsValue value and boolValue are false If the tristate value has value of cancelled, false is returned.

Definition at line 232 of file tristate.h.

operator== [2/2]

bool operator== ( tristate  tsValue, bool  boolValue  )

friend

Equality operator comparing a tristate value tsValue and a bool value boolValue.

Returns

true if both

• both tsValue value and boolValue are true, or
• both tsValue value and boolValue are false If the tristate value has value of cancelled, false is returned.

Definition at line 219 of file tristate.h.

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The documentation for this class was generated from the following file:

• tristate.h