com.google.javascript.rhino.jstype.TernaryValue Maven / Gradle / Ivy
/*
*
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Rhino code, released
* May 6, 1999.
*
* The Initial Developer of the Original Code is
* Netscape Communications Corporation.
* Portions created by the Initial Developer are Copyright (C) 1997-1999
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Bob Jervis
* Google Inc.
*
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* the GNU General Public License Version 2 or later (the "GPL"), in which
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package com.google.javascript.rhino.jstype;
/**
* An enum for ternary logic. The {@link #TRUE} and {@link #FALSE} values
* are equivalent to typical booleans, and the {@link #UNKNOWN} value plays the
* role of a placeholder, which can be either {@link #TRUE} or
* {@link #FALSE}.
*
* A ternary value expression evaluates to {@link #TRUE} or
* {@link #FALSE} only if all replacements of {@link #UNKNOWN} in this
* expression yield the same result. Therefore, the ternary logic coincides
* with typical Boolean logic if the {@link #UNKNOWN} value is not
* present in an expression.
*
* @see Ternary Logic
*/
public enum TernaryValue {
/**
* {@code false}
*/
FALSE {
@Override
public TernaryValue and(TernaryValue that) {
return FALSE;
}
@Override
public TernaryValue not() {
return TRUE;
}
@Override
public TernaryValue or(TernaryValue that) {
return that;
}
@Override
public TernaryValue xor(TernaryValue that) {
return that;
}
@Override
public boolean toBoolean(boolean unknown) {
return false;
}
@Override
public String toString() {
return "false";
}
},
/**
* {@code true}
*/
TRUE {
@Override
public TernaryValue and(TernaryValue that) {
return that;
}
@Override
public TernaryValue not() {
return FALSE;
}
@Override
public TernaryValue or(TernaryValue that) {
return TRUE;
}
@Override
public TernaryValue xor(TernaryValue that) {
return that.not();
}
@Override
public boolean toBoolean(boolean unknown) {
return true;
}
@Override
public String toString() {
return "true";
}
},
/**
* {@code unknown}, it represents lack of knowledge about whether this value
* is {@code true} or {@code false}.
*/
UNKNOWN {
@Override
public TernaryValue and(TernaryValue that) {
return (FALSE.equals(that)) ? FALSE : UNKNOWN;
}
@Override
public TernaryValue not() {
return UNKNOWN;
}
@Override
public TernaryValue or(TernaryValue that) {
return (TRUE.equals(that)) ? TRUE : UNKNOWN;
}
@Override
public TernaryValue xor(TernaryValue that) {
return UNKNOWN;
}
@Override
public boolean toBoolean(boolean unknown) {
return unknown;
}
@Override
public String toString() {
return "unknown";
}
};
/**
* Gets the {@code and} of {@code this} and {@code that}.
*/
public abstract TernaryValue and(TernaryValue that);
/**
* Gets the {@code not} of {@code this}.
*/
public abstract TernaryValue not();
/**
* Gets the {@code or} of {@code this} and {@code that}.
*/
public abstract TernaryValue or(TernaryValue that);
/**
* Gets the {@code xor} of {@code this} and {@code that}.
*/
public abstract TernaryValue xor(TernaryValue that);
/**
* Converts {@code this} ternary value to boolean. The {@code #TRUE} and
* {@code #FALSE} values are simply converted to {@code true} and
* {@code false} respectively, whilst the {@link #UNKNOWN} is converted
* to the specified {@code unknown} value.
*
* @param unknown the boolean value to which the {@link #UNKNOWN} value is
* converted
* @return return
* this == TRUE ? true :
* this == FALSE ? false :
* unknown
*/
public abstract boolean toBoolean(boolean unknown);
/**
* Gets the TernaryValue for the given boolean.
*/
public static TernaryValue forBoolean(boolean val) {
return val ? TernaryValue.TRUE : TernaryValue.FALSE;
}
}