return
true ? 'a' :
false ? 'b' :
'c';
This should return 'a', but it doesn't. It returns 'b' instead. Is there a bug in PHP's order of handling the different parts of the conditional operators?
I got the idea from Are multiple conditional operators in this situation a good idea? where it does seem to work correctly.
(the true and false are for the purpose of the example, of course. in the real code they are statements that evaluate to true and false respectively. yes, i know that for sure)
It is recommended that you avoid
"stacking" ternary expressions. PHP's
behaviour when using more than one
ternary operator within a single
statement is non-obvious
From the PHP Manual under "Non-obvious Ternary Behaviour".
Ternary operators are evaluated left to right, so unless you add it the braces it doesn't behave as you expect. The following would work though,
return (true ? "a" : (false ? "b" : "c"));
Suspect it's evaluating (true ? 'a' : false) as the input to the second ternary operator and interpreting 'a' as true. Try bracketing appropriately.
order of operations:
>>> return true ? 'a' : false ? 'b': 'c';
'b'
>>> return true ? 'a' : (false ? 'b': 'c');
'a'
Let me explain in same way it was explained to me. But you have to pay attention in parenthesis to understand what is happening.
The PHP
The PHP code below
true ? "a" : false ? "b" : "c"
Is equivalent to:
(true ? "a" : false) ? "b" : "c"
Another languages
The code below
true ? "a" : false ? "b" : "c"
Is equivalent to:
true ? "a" : (false ? "b" : "c")
Related
Why is this printing 2?
echo true ? 1 : true ? 2 : 3;
With my understanding, it should print 1.
Why is it not working as expected?
Because what you've written is the same as:
echo (true ? 1 : true) ? 2 : 3;
and as you know 1 is evaluated to true.
What you expect is:
echo (true) ? 1 : (true ? 2 : 3);
So always use braces to avoid such confusions.
As was already written, ternary expressions are left associative in PHP. This means that at first will be executed the first one from the left, then the second and so on.
Separate second ternary clause with parentheses.
echo true ? 1 : (true ? 2 : 3);
Use parentheses when in doubt.
The ternary operator in PHP is left-associative in contrast to other languages and does not work as expected.
from the docs
Example #3 Non-obvious Ternary Behaviour
<?php
// on first glance, the following appears to output 'true'
echo (true?'true':false?'t':'f');
// however, the actual output of the above is 't'
// this is because ternary expressions are evaluated from left to right
// the following is a more obvious version of the same code as above
echo ((true ? 'true' : false) ? 't' : 'f');
// here, you can see that the first expression is evaluated to 'true', which
// in turn evaluates to (bool)true, thus returning the true branch of the
// second ternary expression.
?>
In your case, you should consider the priority of executing statements.
Use following code:
echo true ? 1 : (true ? 2 : 3);
For example,
$a = 2;
$b = 1;
$c = 0;
$result1 = $a ** $b * $c;
// is not equal
$result2 = $a ** ($b * $c);
Are you have used parentheses in expressions in mathematics? - Then, that the result, depending on the execution priority, is not the same. In your case, ternary operators are written without priorities. Let the interpreter understand in what order to perform operations using parentheses.
Late, but a nice example for being carefull from now:
$x = 99;
print ($x === 1) ? 1
: ($x === 2) ? 2
: ($x === 3) ? 3
: ($x === 4) ? 4
: ($x === 5) ? 5
: ($x === 99) ? 'found'
: ($x === 6) ? 6
: 'not found';
// prints out: 6
Result of PHP 7.3.1 (Windows Commandline). I can not understand, why they changed it, because the code becomes really unreadable, if I try to change this.
This question already has answers here:
Stacking Multiple Ternary Operators in PHP
(11 answers)
Closed 4 years ago.
I have a method that I'm checking if param is null, but if I use a ternary operator to make sure the false result isn't a string, I don't get the same expected result... I am a full stack .NET dev by day, but do some PHP free lance and this just stumped me...
$param = null;
// $active evaluates to true
$active = is_null($param) ? true : false;
// $active evaluates to false
$active = is_null($param) ? true : is_string($param)
? (strtolower($param) === 'true')
: true;
I have used nested ternary operators in C# and JavaScript what feels like countless times, but I don't know if I have ever tried in PHP... does PHP attempt to evaluate all nested ternary operations prior to expressing a result or is there something I'm missing here since from my understanding in this case, the ternary operator should be short circuited and evaluated to true in both circumstances.
The ternary operator is left associative unlike most other languages such as C#. The code:
$active = is_null($param)
? true
: is_string($param)
? (strtolower($param) === 'true')
: true;
is evaluated as follows:
$active = ((is_null($param) ? true : is_string($param))
? (strtolower($param) === 'true') : true);
You must explicitly add parenthesis to make sure ?: works the way it does in familiar languages:
$active = is_null($param)
? true
: (is_string($param)
? (strtolower($param) === 'true')
: true);
You need to wrap your second ternary condition with parenthesis (),
<?php
$param = null;
// $active evaluates to true
$active = is_null($param) ? true : false;
echo "Simple ternary result = $active".PHP_EOL;
// $active evaluates to true
$active = is_null($param) ? true : (is_string($param)? (strtolower($param) === 'true'): true);
echo "Nested ternary result = $active";
?>
Note:
It is recommended that you avoid "stacking" ternary expressions. PHP's
behaviour when using more than one ternary operator within a single
statement is non-obvious:
See Example #4 here at http://php.net/manual/en/language.operators.comparison.php
Example #4 Non-obvious Ternary Behaviour
<?php
// on first glance, the following appears to output 'true'
echo (true?'true':false?'t':'f');
// however, the actual output of the above is 't'
// this is because ternary expressions are evaluated from left to right
// the following is a more obvious version of the same code as above
echo ((true ? 'true' : false) ? 't' : 'f');
// here, you can see that the first expression is evaluated to 'true', which
// in turn evaluates to (bool)true, thus returning the true branch of the
// second ternary expression.
?>
DEMO: https://3v4l.org/gW8pk
This is a well-known problem with PHP. I doubt it will ever be fixed. Use parentheses, or if..else or switch statements, to get the behaviour you want.
(In technical terms, the ternary operator in PHP is "left associative", while that in every other language with this operator is "right associative". The latter is the more logical behaviour for this operator.)
This question already has answers here:
Stacking Multiple Ternary Operators in PHP
(11 answers)
Closed 2 years ago.
I was making a clamp() function in php, and decided to go for a nested ternary expression just to try it.
In the end, I settled with this (working) function :
function clamp($value, $min, $max){
return
$value<$min ? $min
: ($value>$max ? $max
: $value);
}
However, why are the brackets around the second expression required? I had tried removing them afterward :..
function clamp($value, $min, $max){
return
$value<$min ? $min
: $value>$max ? $max
: $value;
}
... but in this version, it will return $max if $value is smaller than $min. I just don't understand how it comes to that result.
I had hear of php having "left associativity" with ternary, though I never understood what it meant:
Take
$bool ? "a" : $bool ? "b" : "c"
Right associativity is: $bool ? "a" : ($bool ? "b" : "c")
Left associativity is : ($bool ? "a" : $bool) ? "b" : "c"
So in the end php will always it evaluate to either b or c.
Bonus:
$bool ? $bool ? "c" : "b" : "a"
Here is a syntax that I think wouldn't change meaning based on associativity.
I wonder whether people managed to find a pretty indentation for this variant.
I have an array ...
$a= array(1,2,3,4);
if (expr)
{ echo "if";
}
else
{ echo 'else';
}
When expr is ( $a = '' || $a == 'false') , output is "if" ,
but when expr is ( $a == 'false' || $a = '' ) , output is "else"
Can anyone explain why & how ordering makes a difference ??
Edit : I understand that I am assigning '' to $a. That is not the problem. The real question is : What does the expression $a = '' return? And why does reversing the order of the 2 situations switch us from the IF section to the ELSE section?
AGAIN : I UNDERSTAND I AM ASSIGNING NOT COMPARING. PLEASE ANSWER THE QUESTION AS IS.
First, never use = as a comparison operator. It is an assignment operator.
The difference is that false (as a boolean) is not the same as 'false' as a string.
Certain expressions are type juggled by PHP to evaluate somewhat differently to how you would expect.
false==""
// TRUE.
false=="false"
// FALSE.
Additionally, when you try to compare numbers to strings, PHP will try to juggle the data so that a comparison will be performed. There is a lot to it (much more than I will post here) but you would do well to investigate type juggling and various operators. The docs are a great start for this. You should also have a read of the comparison operators which go into a lot of detail about how various comparisons will work (depending on whether you use == or === for example).
With $a = '' you are setting $a to an empty string. This is the same as:
$a = '';
if($a){
echo 'if';
}
The || operator checks if the first condition is true and if it is, it continues with the code in the brackets. In PHP, if $a is set to anything, it will return true. In the second case $a does not equal the string 'false' (you are not comparing it to a boolean false even!), so it executes the code in the else part.
And Fluffeh is not entirely correct. You can use the assignment operator in an if condition very effectively, you just have to be smart about it.
$a = '' is an assignment: you have, in error, used = in place of ==. Assignment is an expression which has the value of the thing your assigning.
A single equals sign = is the assignment opporator, so $a = '' is assigning an empty string to $a not checking if it is equal to.
In your 1st example you set the value of $a to an empty string, then check if it is false. An empty tring evalutes to false in php, so the conditional is true.
In your second example, you check if $a equals false 1st (when the value of $a is an array), so the conditional is false
Why it doesn't print what is suppose to print?
<?php
$place = 1;
echo $place === 1 ? 'a' : $place === 2 ? 'b' : 'c';
?>
The manual is your friend. Quote:
<?php
// on first glance, the following appears to output 'true'
echo (true?'true':false?'t':'f');
// however, the actual output of the above is 't'
// this is because ternary expressions are evaluated from left to right
// the following is a more obvious version of the same code as above
echo ((true ? 'true' : false) ? 't' : 'f');
// here, you can see that the first expression is evaluated to 'true', which
// in turn evaluates to (bool)true, thus returning the true branch of the
// second ternary expression.
You are basically doing:
echo ($place === 1 ? 'a' : $place === 2) ? 'b' : 'c';
// which is
echo 'a' ? 'b' : 'c';
// which is
echo 'b';
echo ($place === 1 ? 'a' : $place === 2) ? 'b' : 'c';
echo ('a') ? 'b' : 'c';
echo (true) ? 'b' : 'c';
echo 'b';
Thats why.
The conditional operator evaluates from left to right, so you should write
echo ($place === 1 ? 'a' : $place === 2) ? 'b' : 'c';
echo (true ? 'a' : $place === 2) ? 'b' : 'c';
echo 'a' ? 'b' : 'c';
echo true ? 'b' : 'c'; // outputs b
to clarify. This behavior is well-documented.
What do you think it is supposed to print and why, and what is being printed?
Also, from the PHP manual on ternary expressions:
Note:
It is recommended that you avoid "stacking" ternary expressions. PHP's behaviour when using more than one ternary operator within a single statement is non-obvious:
<?php
// on first glance, the following appears to output 'true'
echo (true?'true':false?'t':'f');
// however, the actual output of the above is 't'
// this is because ternary expressions are evaluated from left to right
// the following is a more obvious version of the same code as above
echo ((true ? 'true' : false) ? 't' : 'f');
// here, you can see that the first expression is evaluated to 'true', which
// in turn evaluates to (bool)true, thus returning the true branch of the
// second ternary expression.
?>