Depending upon use case, I would normally use something simple like the following:
abstract class DaysOfWeek
{
const Sunday = 0;
const Monday = 1;
// etc.
}
$today = DaysOfWeek::Sunday;
However, other use cases may require more validation of constants and values. Based on the comments below about reflection, and a few other notes, here's an expanded example which may better serve a much wider range of cases:
abstract class BasicEnum {
private static $constCacheArray = NULL;
private static function getConstants() {
if (self::$constCacheArray == NULL) {
self::$constCacheArray = [];
}
$calledClass = get_called_class();
if (!array_key_exists($calledClass, self::$constCacheArray)) {
$reflect = new ReflectionClass($calledClass);
self::$constCacheArray[$calledClass] = $reflect->getConstants();
}
return self::$constCacheArray[$calledClass];
}
public static function isValidName($name, $strict = false) {
$constants = self::getConstants();
if ($strict) {
return array_key_exists($name, $constants);
}
$keys = array_map('strtolower', array_keys($constants));
return in_array(strtolower($name), $keys);
}
public static function isValidValue($value, $strict = true) {
$values = array_values(self::getConstants());
return in_array($value, $values, $strict);
}
}
By creating a simple enum class that extends BasicEnum, you now have the ability to use methods thusly for simple input validation:
abstract class DaysOfWeek extends BasicEnum {
const Sunday = 0;
const Monday = 1;
const Tuesday = 2;
const Wednesday = 3;
const Thursday = 4;
const Friday = 5;
const Saturday = 6;
}
DaysOfWeek::isValidName('Humpday'); // false
DaysOfWeek::isValidName('Monday'); // true
DaysOfWeek::isValidName('monday'); // true
DaysOfWeek::isValidName('monday', $strict = true); // false
DaysOfWeek::isValidName(0); // false
DaysOfWeek::isValidValue(0); // true
DaysOfWeek::isValidValue(5); // true
DaysOfWeek::isValidValue(7); // false
DaysOfWeek::isValidValue('Friday'); // false
As a side note, any time I use reflection at least once on a static/const class where the data won't change (such as in an enum), I cache the results of those reflection calls, since using fresh reflection objects each time will eventually have a noticeable performance impact (Stored in an assocciative array for multiple enums).
Now that most people have finally upgraded to at least 5.3, and SplEnum
is available, that is certainly a viable option as well--as long as you don't mind the traditionally unintuitive notion of having actual enum instantiations throughout your codebase. In the above example, BasicEnum
and DaysOfWeek
cannot be instantiated at all, nor should they be.
Yes, it was added in version 2.5. The expression syntax is:
a if condition else b
First condition
is evaluated, then exactly one of either a
or b
is evaluated and returned based on the Boolean value of condition
. If condition
evaluates to True
, then a
is evaluated and returned but b
is ignored, or else when b
is evaluated and returned but a
is ignored.
This allows short-circuiting because when condition
is true only a
is evaluated and b
is not evaluated at all, but when condition
is false only b
is evaluated and a
is not evaluated at all.
For example:
>>> 'true' if True else 'false'
'true'
>>> 'true' if False else 'false'
'false'
Note that conditionals are an expression, not a statement. This means you can't use assignment statements or pass
or other statements within a conditional expression:
>>> pass if False else x = 3
File "<stdin>", line 1
pass if False else x = 3
^
SyntaxError: invalid syntax
You can, however, use conditional expressions to assign a variable like so:
x = a if True else b
Think of the conditional expression as switching between two values. It is very useful when you're in a 'one value or another' situation, it but doesn't do much else.
If you need to use statements, you have to use a normal if
statement instead of a conditional expression.
Keep in mind that it's frowned upon by some Pythonistas for several reasons:
- The order of the arguments is different from those of the classic
condition ? a : b
ternary operator from many other languages (such as C, C++, Go, Perl, Ruby, Java, Javascript, etc.), which may lead to bugs when people unfamiliar with Python's "surprising" behaviour use it (they may reverse the argument order).
- Some find it "unwieldy", since it goes contrary to the normal flow of thought (thinking of the condition first and then the effects).
- Stylistic reasons. (Although the 'inline
if
' can be really useful, and make your script more concise, it really does complicate your code)
If you're having trouble remembering the order, then remember that when read aloud, you (almost) say what you mean. For example, x = 4 if b > 8 else 9
is read aloud as x will be 4 if b is greater than 8 otherwise 9
.
Official documentation:
Best Answer
When your first argument is null, they're basically the same except that the null coalescing won't output an
E_NOTICE
when you have an undefined variable. The PHP 7.0 migration docs has this to say:Here's some example code to demonstrate this:
The lines that have the notice are the ones where I'm using the shorthand ternary operator as opposed to the null coalescing operator. However, even with the notice, PHP will give the same response back.
Execute the code: https://3v4l.org/McavC
Of course, this is always assuming the first argument is
null
. Once it's no longer null, then you end up with differences in that the??
operator would always return the first argument while the?:
shorthand would only if the first argument was truthy, and that relies on how PHP would type-cast things to a boolean.So:
would then have
$a
be equal tofalse
and$b
equal to'g'
.