tristate Class Reference

#include <tristate.h>

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 Qt 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 QDialog to get some validation from a user. While QDialog::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 QDialog::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 97 of file tristate.h.

Public Member Functions

tristate ()

Default constructor, object has cancelled value set.

tristate (bool boolValue)

Constructor accepting a boolean value.

tristate (char c)

Constructor accepting a char value.

tristate (int intValue)

Constructor accepting an integer value.

bool operator! () const

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

bool operator~ () const

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

tristate & operator= (const tristate &tsValue)

QString toString () const

Friends

bool operator== (bool boolValue, tristate tsValue)

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

bool operator== (tristate tsValue, bool boolValue)

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

bool operator!= (bool boolValue, tristate tsValue)

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

bool operator!= (tristate tsValue, bool boolValue)

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

Constructor & Destructor Documentation

tristate::tristate ( ) [inline]

Default constructor, object has cancelled value set.

Definition at line 103 of file tristate.h.

tristate::tristate ( bool boolValue ) [inline]

Constructor accepting a boolean value.

Definition at line 111 of file tristate.h.

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 123 of file tristate.h.

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 134 of file tristate.h.

Member Function Documentation

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 143 of file tristate.h.

tristate& tristate::operator= ( const tristate & tsValue ) [inline]

Definition at line 151 of file tristate.h.
References m_value.

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 149 of file tristate.h.

QString tristate::toString ( ) const [inline]

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

Definition at line 164 of file tristate.h.
Referenced by SQLite2ToSQLite3Migration::cancelClicked(), KexiBLOBBuffer::objectForId(), SQLite2ToSQLite3Migration::processExited(), and KexiTableDesignerView::storeData().

Friends And Related Function Documentation

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 204 of file tristate.h.

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 194 of file tristate.h.

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 217 of file tristate.h.

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 230 of file tristate.h.

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

tristate.h


Public Member Functions
	tristate ()
	Default constructor, object has cancelled value set.
	tristate (bool boolValue)
	Constructor accepting a boolean value.
	tristate (char c)
	Constructor accepting a char value.
	tristate (int intValue)
	Constructor accepting an integer value.
bool	operator! () const
	Casting to bool type with negation: true is only returned if the original tristate value is equal to false.
bool	operator~ () const
	Special casting to bool type: true is only returned if the original tristate value is equal to cancelled.
tristate &	operator= (const tristate &tsValue)
QString	toString () const
Friends
bool	operator== (bool boolValue, tristate tsValue)
	Equality operator comparing a bool value `boolValue` and a tristate value `tsValue`.
bool	operator== (tristate tsValue, bool boolValue)
	Equality operator comparing a tristate value `tsValue` and a bool value `boolValue`.
bool	operator!= (bool boolValue, tristate tsValue)
	Inequality operator comparing a bool value `boolValue` and a tristate value `tsValue`.
bool	operator!= (tristate tsValue, bool boolValue)
	Inequality operator comparing a tristate value `tsValue` and a bool value `boolValue`.

Kexi API Documentation (2.0 alpha)

tristate Class Reference

Detailed Description

Public Member Functions

Friends

Constructor & Destructor Documentation

Member Function Documentation

Friends And Related Function Documentation