$a = '';
$b = 1;
How to print $b if $a = '' using shorthand in PHP?
in javascript there is something like
a || b;
Ternary Operator
$a = '';
$b = 1;
echo $a ?: $b; // 1
Until $a is evaluated false, $b will be displayed. Remember that the following things are considered to be empty:
"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
$var; (a variable declared, but without a value)
That means that if $a is "", 0, "0", null, false, array(), .. then $b will be displayed. See PHP type comparison tables.
If you want to display $b only when $a is an empty string, then you should uses strict comparison operators (===)
$a = '';
$b = 1;
echo $a === '' ? $b : ''; // 1
This is the shorthand for an IF/Else statement in PHP.
echo ($a != '' ? $a : $b)
If $a is not an empty string output (echo) $a otherwise output $b.
As others ahve said Turnary operator is handy for most senarios.
echo $a ?: $b;//b
But it is NOT shorthand for empty().
Ternary operator will issue notices if var/array keys/properties are not set.
echo $someArray['key that doesnt exist'] ?: $b;//Notice: Undefined index
echo $arrayThatDoesntExist['key-that-doesnt-exist'] ?: $b;//Notice: Undefined variable
empty() will take care of the additional checks for you and its recomended to just use it.
if (empty($arrayThatDoesntExist['key-that-doesnt-exist'])) echo $b;
You could technically just suppress the warning/notice with # and the ternary operator becomes a replacement for empty().
#echo $someArray['key that doesnt exist'] ?: $b;
#echo $arrayThatDoesntExist['key-that-doesnt-exist'] ?: $b;
But usually not recommended as supressing notices and warnings could lead you into trouble later on plus I think it may have some performance impact.
Related
I'm working on a new project and I've come upon the question if the ternary short hand operator the same as using the traditional ternary in combination with the empty() function?
For clarity purposes my question is if: $a ?: $b is the same as !empty($a) ? $a : $b ?
$a ?: $b is short-hand for $a ? $a : $b which is not quite the same as !empty($a) ? $a : $b
The difference between them requires careful reading of the definition of the empty pseudo-function:
Determine whether a variable is considered to be empty. A variable is considered empty if it does not exist or if its value equals false. empty() does not generate a warning if the variable does not exist.
When you just use $a "in boolean context", as in if ( $a ) or $a ? $a : $b or $a ?: $b, its value will be converted to boolean. If the variable doesn't exist - a mistyped variable name, for instance - a Warning will be issued while retrieving that value.
The special power of the empty() pseudo-function is that it won't give you that Warning. The actual result will be the same - an unset variable is considered "equal to false" - but the two pieces of code aren't always interchangeable.
Let's say I want to check for a couple of different parameters, and then fall back to a default value, is there a way to do it without ugly and verbose writing of isset()?
For example in JS we can do:
var someVariable = otherVar || anotherVar || 'fallback here';
The equivalent in PHP would be something like:
$someVariable = (isset($otherVar) ? $otherVar : (isset($anotherVar) ? $anotherVar : 'fallback here'));
which is obviously a mess and horrible to read.
Lots of solutions exist for single fallbacks, i.e.:
$someVariable = $otherVar ?: 'fallback here';
but that doesn't help me with requiring more than one in the line of checks.
Given that I am only interested in whether or not the value is set or truth-y (i.e. I am happy for 1 to be accepted as the used value, and for 0/false/null to be skipped and for the next parameter in the chain to be used), what is the best way to avoid the undefined index warning?
In reality, I would be doing this on arrays in most cases, but not all, and it's probably that they will be different arrays. I may want to use $_POST for the first, then check $_GET under a different key, and then fall back to a default string for example.
Ignoring PHP warnings and notices is not a good idea at all.
But just for the experiment, I can suggest you the error control operator #.
PHP supports one error control operator: the at sign (#). When prepended to an expression in PHP, any error messages that might be generated by that expression will be ignored.
$someVariable = #$otherVar ? #$var : 'fallback here';
echo $someVariable;
// output: fallback here
http://php.net/manual/en/language.operators.errorcontrol.php
You can chain ?: but you'll still need to suppress errors with #.
For example, the following will work similarly to your JavaScript example:
$foo = #$bar ?: #$baz ?: #$qux ?: "I give up";
It's the equivalent of multiple "single fallbacks":
$foo = (#$bar ?: (#$baz ?: (#$qux ?: "I give up")));
Be careful though, ?: only checks for truthyness. There are scenarios where isset() and truthyness do not agree. Additionally, ?: fallback functionality was introduced in PHP 5.3.
If you only care about nullness and have PHP 7 available, it introduced a null coalescing operator.
This is ambiguous and it is deprecated...
$something = $a ? $b : $c ?: $d;
So, you have 2 alternatives for grouping:
$something = $a ? $b : ($c ?: $d); // version 1
$something = ($a ? $b : $c) ?: $d; // version 2
Which one is correct? Let's test this...
$posibilities = [TRUE, FALSE, NULL, [], new stdClass()];
$v1_is_correct = TRUE;
$v2_is_correct = TRUE;
foreach ($posibilities as $a) {
foreach ($posibilities as $b) {
foreach ($posibilities as $c) {
foreach ($posibilities as $d) {
$original = (int)($a ? $b : $c ?: $d);
$v1 = (int)($a ? $b : ($c ?: $d));
$v2 = (int)(($a ? $b : $c) ?: $d);
$v1_is_correct = $v1_is_correct && ($original === $v1);
$v2_is_correct = $v2_is_correct && ($original === $v2);
print "ORIG: $original - V1: $v1 - V2: $v2 \n";
}
}
}
}
print "\n";
$v1_is_correct ? print "V1 is correct \n" : NULL;
$v2_is_correct ? print "V2 is correct \n" : NULL;
Result: V2 is correct.
$a ? $b : $c ?: $d
is equivalent to...
($a ? $b : $c) ?: $d
I found this question at http://www.phpinterviewquestions.com/php-interview-questions/operator-precedence/
Following operations are true or false? (Operator Precedence)
$one = true;
$two = null;
$a = isset($one) && isset($two);
$b = isset($one) and isset($two);
echo $a.'<br>';
echo $b;
I tried the above code. But only $b gets echoed as 1 (which is true). $a is not getting echoed. What could be the reason? I was expecting $a to be 0 (false).
It's not about precedence, it's about implicit type casting
Use var_dump($a); instead of echo $a;
$a actually is false, but being echo'ed false is casted to empty string.
Javascript employs the conjunction and disjunction operators.
The left–operand is returned if it can be evaluated as: false, in the case of conjunction (a && b), or true, in the case of disjunction (a || b); otherwise the right–operand is returned.
Do equivalent operators exist in PHP?
PHP supports short-circuit evaluation, a little different from JavaScript's conjunction. We often see the example (even if it isn't good practice) of using short-circuit evaluation to test the result of a MySQL query in PHP:
// mysql_query() returns false, so the OR condition (die()) is executed.
$result = mysql_query("some faulty query") || die("Error");
Note that short-circuit evaluation works when in PHP when there is an expression to be evaluated on either side of the boolean operator, which would produce a return value. It then executes the right side only if the left side is false. This is different from JavaScript:
Simply doing:
$a || $b
would return a boolean value TRUE or FALSE if either is truthy or both are falsy. It would NOT return the value of $b if $a was falsy:
$a = FALSE;
$b = "I'm b";
echo $a || $b;
// Prints "1", not "I'm b"
So to answer the question, PHP will do a boolean comparison of the two values and return the result. It will not return the first truthy value of the two.
More idiomatically in PHP (if there is such a thing as idiomatic PHP) would be to use a ternary operation:
$c = $a ? $a : $b;
// PHP 5.3 and later supports
$c = $a ?: $b;
echo $a ?: $b;
// "I'm b"
Update for PHP 7
PHP 7 introduces the ?? null coalescing operator which can act as a closer approximation to conjunction. It's especially helpful because it doesn't require you to check isset() on the left operand's array keys.
$a = null;
$b = 123;
$c = $a ?? $b;
// $c is 123;
Javascript employs the conjunction and disjunction operators.
The left–operand is returned if it can be evaluated as: false, in the case of conjunction (a && b), or true, in the case of disjunction (a || b); otherwise the right–operand is returned.
Do equivalent operators exist in PHP?
PHP supports short-circuit evaluation, a little different from JavaScript's conjunction. We often see the example (even if it isn't good practice) of using short-circuit evaluation to test the result of a MySQL query in PHP:
// mysql_query() returns false, so the OR condition (die()) is executed.
$result = mysql_query("some faulty query") || die("Error");
Note that short-circuit evaluation works when in PHP when there is an expression to be evaluated on either side of the boolean operator, which would produce a return value. It then executes the right side only if the left side is false. This is different from JavaScript:
Simply doing:
$a || $b
would return a boolean value TRUE or FALSE if either is truthy or both are falsy. It would NOT return the value of $b if $a was falsy:
$a = FALSE;
$b = "I'm b";
echo $a || $b;
// Prints "1", not "I'm b"
So to answer the question, PHP will do a boolean comparison of the two values and return the result. It will not return the first truthy value of the two.
More idiomatically in PHP (if there is such a thing as idiomatic PHP) would be to use a ternary operation:
$c = $a ? $a : $b;
// PHP 5.3 and later supports
$c = $a ?: $b;
echo $a ?: $b;
// "I'm b"
Update for PHP 7
PHP 7 introduces the ?? null coalescing operator which can act as a closer approximation to conjunction. It's especially helpful because it doesn't require you to check isset() on the left operand's array keys.
$a = null;
$b = 123;
$c = $a ?? $b;
// $c is 123;