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I'm personally an advocate of the ternary operator: () ? :
I do realize that it has its place, but I have come across many programmers that are completely against ever using it, and some that use it too often.
What are your feelings on it? What interesting code have you seen using it?
Use it for simple expressions only:
int a = (b > 10) ? c : d;
Don't chain or nest ternary operators as it hard to read and confusing:
int a = b > 10 ? c < 20 ? 50 : 80 : e == 2 ? 4 : 8;
Moreover, when using ternary operator, consider formatting the code in a way that improves readability:
int a = (b > 10) ? some_value
: another_value;
It makes debugging slightly more difficult since you can not place breakpoints on each of the sub expressions. I use it rarely.
I love them, especially in type-safe languages.
I don't see how this:
int count = (condition) ? 1 : 0;
is any harder than this:
int count;
if (condition)
{
count = 1;
}
else
{
count = 0;
}
I'd argue that ternary operators make everything less complex and more neat than the alternative.
Chained I'm fine with - nested, not so much.
I tend to use them more in C simply because they're an if statement that has value, so it cuts down on unnecessary repetition or variables:
x = (y < 100) ? "dog" :
(y < 150) ? "cat" :
(y < 300) ? "bar" : "baz";
rather than
if (y < 100) { x = "dog"; }
else if (y < 150) { x = "cat"; }
else if (y < 300) { x = "bar"; }
else { x = "baz"; }
In assignments like this, I find it's less to refactor, and clearer.
When I'm working in ruby on the other hand, I'm more likely to use if...else...end because it's an expression too.
x = if (y < 100) then "dog"
elif (y < 150) then "cat"
elif (y < 300) then "bar"
else "baz"
end
(Although, admittedly, for something this simple, I might just use the ternary operator anyway.)
The ternary ?: operator is merely a functional equivalent of the procedural if construct. So as long as you are not using nested ?: expressions, the arguments for/against the functional representation of any operation applies here. But nesting ternary operations can result in code that is downright confusing (exercise for the reader: try writing a parser that will handle nested ternary conditionals and you will appreciate their complexity).
But there are plenty of situations where conservative use of the ?: operator can result in code that is actually easier to read than otherwise. For example:
int compareTo(Object object) {
if((isLessThan(object) && reverseOrder) || (isGreaterThan(object) && !reverseOrder)) {
return 1;
if((isLessThan(object) && !reverseOrder) || (isGreaterThan(object) && reverseOrder)) {
return -1;
else
return 0;
}
Now compare that with this:
int compareTo(Object object) {
if(isLessThan(object))
return reverseOrder ? 1 : -1;
else(isGreaterThan(object))
return reverseOrder ? -1 : 1;
else
return 0;
}
As the code is more compact, there is less syntactic noise, and by using the ternary operator judiciously (that is only in relation with the reverseOrder property) the end result isn't particularly terse.
It's a question of style, really; the subconscious rules I tend to follow are:
Only evaluate 1 expression - so foo = (bar > baz) ? true : false, but NOT foo = (bar > baz && lotto && someArray.Contains(someValue)) ? true : false
If I'm using it for display logic, e.g. <%= (foo) ? "Yes" : "No" %>
Only really use it for assignment; never flow logic (so never (foo) ? FooIsTrue(foo) : FooIsALie(foo) ) Flow logic in ternary is itself a lie, ignore that last point.
I like it because it's concise and elegant for simple assignment operations.
Like so many opinion questions, the answer is inevitably: it depends
For something like:
return x ? "Yes" : "No";
I think that is much more concise (and quicker for me to parse) than:
if (x) {
return "Yes";
} else {
return "No";
}
Now if your conditional expression is complex, then the ternary operation is not a good choice. Something like:
x && y && z >= 10 && s.Length == 0 || !foo
is not a good candidate for the ternary operator.
As an aside, if you are a C programmer, GCC actually has an extension that allows you to exclude the if-true portion of the ternary, like this:
/* 'y' is a char * */
const char *x = y ? : "Not set";
Which will set x to y assuming y is not NULL. Good stuff.
In my mind, it only makes sense to use the ternary operator in cases where an expression is needed.
In other cases, it seems like the ternary operator decreases clarity.
I use the ternary operator wherever I can, unless it makes the code extremely hard to read, but then that's usually just an indication that my code could use a little refactoring.
It always puzzles me how some people think the ternary operator is a "hidden" feature or is somewhat mysterious. It's one of the first things I learnt when I start programming in C, and I don't think it decreases readability at all. It's a natural part of the language.
By the measure of cyclomatic complexity, the use of if statements or the ternary operator are equivalent. So by that measure, the answer is no, the complexity would be exactly the same as before.
By other measures such as readability, maintainability, and DRY (don't repeat yourself), either choice may prove better than the other.
I use it quite often in places where I'm constrained to work in a constructor - for example, the new .NET 3.5 LINQ to XML constructs - to define default values when an optional parameter is null.
Contrived example:
var e = new XElement("Something",
param == null ? new XElement("Value", "Default")
: new XElement("Value", param.ToString())
);
or (thanks asterite)
var e = new XElement("Something",
new XElement("Value",
param == null ? "Default"
: param.ToString()
)
);
No matter whether you use the ternary operator or not, making sure your code is readable is the important thing. Any construct can be made unreadable.
I agree with jmulder: it shouldn't be used in place of a if, but it has its place for return expression or inside an expression:
echo "Result: " + n + " meter" + (n != 1 ? "s" : "");
return a == null ? "null" : a;
The former is just an example, and better internationalisation and localisation support of plural should be used!
If you're using the ternary operator for a simple conditional assignment I think it's fine. I've seen it (ab)used to control program flow without even making an assignment, and I think that should be avoided. Use an if statement in these cases.
(Hack of the day)
#define IF(x) x ?
#define ELSE :
Then you can do if-then-else as expression:
int b = IF(condition1) res1
ELSE IF(condition2) res2
ELSE IF(conditions3) res3
ELSE res4;
I think the ternary operator should be used when needed. It is obviously a very subjective choice, but I find that a simple expression (specially as a return expression) is much clearer than a full test. Example in C/C++:
return (a>0)?a:0;
Compared to:
if(a>0) return a;
else return 0;
You also have the case where the solution is between the ternary operator and creating a function. For example in Python:
l = [ i if i > 0 else 0 for i in lst ]
The alternative is:
def cap(value):
if value > 0:
return value
return 0
l = [ cap(i) for i in lst ]
It is needed enough that in Python (as an example), such an idiom could be seen regularly:
l = [ ((i>0 and [i]) or [0])[0] for i in lst ]
this line uses properties of the logical operators in Python: they are lazy and returns the last value computed if it is equal to the final state.
I've seen such beasts like (it was actually much worse since it was isValidDate and checked month and day as well, but I couldn't be bothered trying to remember the whole thing):
isLeapYear =
((yyyy % 400) == 0)
? 1
: ((yyyy % 100) == 0)
? 0
: ((yyyy % 4) == 0)
? 1
: 0;
where, plainly, a series of if-statements would have been better (although this one's still better than the macro version I once saw).
I don't mind it for small things like:
reportedAge = (isFemale && (Age >= 21)) ? 21 + (Age - 21) / 3 : Age;
or even slightly tricky things like:
printf ("Deleted %d file%s\n", n, (n == 1) ? "" : "s");
I like using the operator in debug code to print error values so I don't have to look them up all the time. Usually I do this for debug prints that aren't going to remain once I'm done developing.
int result = do_something();
if( result != 0 )
{
debug_printf("Error while doing something, code %x (%s)\n", result,
result == 7 ? "ERROR_YES" :
result == 8 ? "ERROR_NO" :
result == 9 ? "ERROR_FILE_NOT_FOUND" :
"Unknown");
}
I almost never use the ternary operator, because whenever I do use it, it always makes me think a lot more than I have to later when I try to maintain it.
I like to avoid verbosity, but when it makes the code a lot easier to pick up, I will go for the verbosity.
Consider:
String name = firstName;
if (middleName != null) {
name += " " + middleName;
}
name += " " + lastName;
Now, that is a bit verbose, but I find it a lot more readable than:
String name = firstName + (middleName == null ? "" : " " + middleName)
+ " " + lastName;
Or:
String name = firstName;
name += (middleName == null ? "" : " " + middleName);
name += " " + lastName;
It just seems to compress too much information into too little space, without making it clear what's going on. Every time I saw the ternary operator used, I have always found an alternative that seemed much easier to read... then again, that is an extremely subjective opinion, so if you and your colleagues find ternary very readable, go for it.
I like them. I don't know why, but I feel very cool when I use the ternary expression.
I treat ternary operators a lot like GOTO. They have their place, but they are something which you should usually avoid to make the code easier to understand.
Well, the syntax for it is horrid. I find functional ifs very useful, and they often makes code more readable.
I would suggest making a macro to make it more readable, but I'm sure someone can come up with a horrible edge case (as there always is with C++).
I typically use it in things like this:
before:
if(isheader)
drawtext(x, y, WHITE, string);
else
drawtext(x, y, BLUE, string);
after:
drawtext(x, y, isheader == true ? WHITE : BLUE, string);
As others have pointed out they are nice for short simple conditions. I especially like them for defaults (kind of like the || and or usage in JavaScript and Python), e.g.
int repCount = pRepCountIn ? *pRepCountIn : defaultRepCount;
Another common use is to initialize a reference in C++. Since references have to be declared and initialized in the same statement you can't use an if statement.
SomeType& ref = pInput ? *pInput : somethingElse;
I like Groovy's special case of the ternary operator, called the Elvis operator: ?:
expr ?: default
This code evaluates to expr if it's not null, and default if it is. Technically it's not really a ternary operator, but it's definitely related to it and saves a lot of time/typing.
I recently saw a variation on ternary operators (well, sort of) that make the standard "() ? :" variant seem to be a paragon of clarity:
var Result = [CaseIfFalse, CaseIfTrue][(boolean expression)]
or, to give a more tangible example:
var Name = ['Jane', 'John'][Gender == 'm'];
Mind you, this is JavaScript, so things like that might not be possible in other languages (thankfully).
Only when:
$var = (simple > test ? simple_result_1 : simple_result_2);
KISS.
For simple if cases, I like to use it. Actually it's much easier to read/code for instance as parameters for functions or things like that. Also to avoid the new line I like to keep with all my if/else.
Nesting it would be a big no-no in my book.
So, resuming, for a single if/else I'll use the ternary operator. For other cases, a regular if/else if/else (or switch).
For simple tasks, like assigning a different value depending on a condition, they're great. I wouldn't use them when there are longer expressions depending on the condition though.
If you and your workmates understand what they do and they aren't created in massive groups I think they make the code less complex and easier to read because there is simply less code.
The only time I think ternary operators make code harder to understand is when you have more than three or foyr in one line. Most people don't remember that they are right based precedence and when you have a stack of them it makes reading the code a nightmare.
As so many answers have said, it depends. I find that if the ternary comparison is not visible in a quick scan down the code, then it should not be used.
As a side issue, I might also note that its very existence is actually a bit of an anomaly due to the fact that in C, comparison testing is a statement. In Icon, the if construct (like most of Icon) is actually an expression. So you can do things like:
x[if y > 5 then 5 else y] := "Y"
... which I find much more readable than a ternary comparison operator. :-)
There was a discussion recently about the possibility of adding the ?: operator to Icon, but several people correctly pointed out that there was absolutely no need because of the way if works.
Which means that if you could do that in C (or any of the other languages that have the ternary operator), then you wouldn't, in fact, need the ternary operator at all.
Related
Almost all programming languages are having the concept of logical operator
I am having a query why logical operators were created. I googled and found its created for condition based operation, but that's a kind of usage i think.
I am interested in the answer that what are the challenges people faced without this operator. Please explain with example if possible.
I am interested in the answer that what are the challenges people faced without this operator.
Super-verbose deeply nested if() conditions, and especially loop conditions.
while (a && b) {
a = something;
b = something_else;
}
written without logical operators becomes:
while (a) {
if (!b) break; // or if(b){} else break; if you want to avoid logical ! as well
a = something;
b = something_else;
}
Of if you don't want a loop, do you want to write this?
if (c >= 'a') {
if (c <= 'z') {
stuff;
}
}
No, of course you don't because it's horrible compared to if (c >= 'a' && c <= 'z'), especially if there's an else, or this is inside another nesting. Especially if your coding-style rules require 8-space indentation for each level of nesting, or the { on its own line making each level of nesting eat up even more vertical space.
Note that a&b is not equivalent to a&&b: even apart from short-circuit evaluation. (Where b isn't even evaluated if a is false.) e.g. 2 & 1 is false, because their integer bit patterns don't have any of the same bits set.
Short-circuit evaluation allows loop conditions like while(p && p->data != 0) to check for a NULL pointer and then conditionally do something only on non-NULL.
Compact expressions were a big deal when computers were programmed over slow serial lines using paper teletypes.
Also note that these are purely high-level language-design considerations. CPU hardware doesn't have anything like logical operators; it usually takes multiple instructions to implement a ! on an integer (into a 0/1 integer, not when used as an if condition).
if (a && b) typically compiles to two test/branch instructions in a row.
I'd like to ask what is the general opinion about using 2 Ternary operators instead of an if/else block for 2 variables.
Giving an example to make it clearer,
The if/else block:
var foo;
var bar;
if (boolean_expression) {
foo = value1;
bar = value2;
} else {
foo = value3;
bar = value4;
}
Using 2 Ternary Operations:
var foo = (boolean_expression) ? value1 : value3;
var bar= (boolean_expression) ? value2 : value4;
Obviously the if/else block is more efficient, since it only evaluates the boolean_expression once, whereas the 2 ternary operations evaluate it twice.
However, using ternary operations is, in my opinion, so much cleaner and readable, that I've recently decided on sacrificing the minimal efficiency difference between the two of them to improve my code's readability. (Provided the code isn't critical or executed too frequently)
Also, I would weakly argue the same for 3 variables.
Am I doing a horrible thing to my code, or is there a better way I'm not aware?
I'm coding in c#, but I guess this question matters for any language that has the ternary operation.
I guess this question matters for any language that has the ternary
operation
Some languages provide this:
(foo, bar) = (boolean_expression) ? (value1, value2) : (value3, value4);
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Explain: This question is more about the design intentions of Kotlin. Many expression languages support both Ternary operator and if expression [e.g., Ruby, Groovy.]
First of all, I know Groovy supports both Ternary operator and Elvis operator: Ternary operator in Groovy. So I don't think it's a syntax problem.
Then the official documents said:
In Kotlin, if is an expression, i.e. it returns a value. Therefore there is no ternary operator (condition ? then : else), because ordinary if works fine in this role.
And this doesn't convince me. Because Kotlin support Elvis operator which ordinary if works just fine in that role either.
I think ternary operator is sometimes better than ordinary if, though I wonder why doesn't Kotlin just support ternary operator?
In languages which have ternary operator you use it like this
String value = condition ? foo : bar;
In Kotlin you can do the same thing using if and else
var value = if(condition) foo else bar;
Its bit verbose than the ternary operator. But designers of Kotlin have thought it is ok. You can use if-else like this because in Kotlin if is an expression and returns a value
Elvis operator is essentially a compressed version of ternary conditional statement and equivalent to following in Kotlin.
var value = if(foo != null) foo else bar;
But if Elvis operator is used it simplify as follows
var value = foo ?: bar;
This is considerable simplification and Kotlin decided to keep it.
Because if .. else .. works fine. Take a look:
fun main(args: Array<String>) {
var i = 2
println("i ${ if(i == 1) "equals 1" else "not equals 1" }")
}
Ternary operator has its problems, for example it is hard to read with big expressions. Here is a line from my C++ project where I used ternary operator:
const long offset = (comm_rank > 0) ? task_size_mod + (comm_rank - 1) * task_size : 0;
I would rather use an if else expression here since it is so much more visible.
Answering you question, I am aware of two reasons why ternary operator was not implemented in Kotlin:
1) Since if else is an expression anyway, it can replace ? :
2) Experience from other languages (C++) shows that ? : provokes hard-to-read code, so it is better to be left out
Programmers at some point, have to make a decision to execute a block of code, this is known as Control Flow. If statement is most basic way to control flow in Kotlin. Important point to note that in Kotlin, If is an expression not a statement as it is Java.
Statement: A statement is an executed line which does not return a
value. As a result, statement cannot sit right side of an equal
sign.
Expression: An expression returns a value.So the result of a Kolin
If expression can be assigned to a variable.
Because of this the ternary expression would be redundant and does not exists in Kotlin. In Java we would write (Here is the answer of your question)
For Example
Ternary Operator in Java
int lowest = (a < b) ? a : b;
In Kotlin we can write something similar using the if expression.
val lowest = if(a < b) a else b
NOTE:
When If is used as an expression it must contain an else clause. The expression must have a value in all case.
Because if-else is an expression in Kotlin :
String check = number % 2 == 0 ? "even" : "odd" // Java
if (number % 2 == 0) "even else "odd" // Kotlin
So that's why there are no ternary operator in Kotlin, Moreover you can use when expressions too, it's so handy if you want to provide a lot of possible execution paths
I've been wondering myself multiple times if, and if not, why not, there is an idiom/shortcut for the following pseudocode:
if object.value == some_value then object.value = some_other_value
For example, in JavaScript I sometimes write:
if (document.getElementById("toggledDiv").style.display == "block") {
document.getElementById("toggledDiv").style.display = "none";
}
This seems to be rather tedious. Is there a name for this idiom, and is there a more concise syntax for this in common programming languages?
Thank you!
Edit: To be more precise, I don't care about the braces, but about that you have to reference the attribute at least to times. I'd like to have something like that (pseudocode):
test ( object.value ):
if (it > 0) it = 0;
else it -= 1;
e. g.:
test (document.getElementById("toggledDiv").style.display):
if (it == "block") it = "none";
where it is a keyword that references the tested property. I'm just wondering no programming language seems to have implemented that.
Upate:
Okay, in the meantime I have found something which is a little bit short, but only works in JavaScript:
(function(s){
if(s.display=='block')
s.display="none";
else
s.display='block';
})(document.getElementById("toggledDiv").style)
Well, in Haskell, and other FP languages, conditionals, like ternary operators, are first-class expressions, so you can float the assignment out,
a = if x == y then x else z
Making the code a lot cleaner.
I don't know of any languages that support it out of the box, but there are a number that support defining new operators. In theory, you could write something like the following (in psuedo-code)
operator <T> T toggle(T value, T[] values) {
for(int i=0; i<values.size(); i++) {
if(value == values[i]) {
if(values.size() > (i+1)) {
return values[i+1]
} else {
return values[0]
}
}
}
error "value $value not found in value list $values"
}
Assuming my psuedo-code is correct, this would allow you to do the following:
v = true;
v = v toggle [true, false] ; // v == false
v = v toggle [true, false] ; // v == true (loops to beginning of list
v = v toggle [false, true, true] ; // v == true, since true is both the 2nd and 3rd elements of the list
You could also two versions:
One that, if the values isn't in the list, returns the original value
One that, if the values isn't in the list, throws an error (what my version did)
The former would be less of a toggle and more of... what you asked for, I guess. I was basing the code off the toggle use case from the previous note about css/block/none, where toggle is the more common behavior.
Assuming the language supports it, you could write a toggle= operator too:
v toggle= ['none', 'block']
In JavaScript you can do:
var d = document.getElementById("toggledDiv");
if (d.style.display == "block") d.style.display = "none";
Is there a programming language that supports chained notation a < b < c to be used instead of a < b and b < c in conditional statements?
Example:
if ( 2 < x < 5 )
if ( 2 < x && x < 5 )
First statementlooks better to me, it's easier to understand and the compiler could use transitivity property to warn about mistakes (e.g. 5 < x < 2 would give a warning).
Python does that.
Icon does this, and it is not part of any hacky special-case "chaining"; it is part of Icon's goal-directed evaluation model. Any comparison either succeeds or fails. If it succeeds, it produces the right-hand side. So you can write
if 0 <= i <= j < n then ...
and it works exactly the way you would expect. But it works not just for comparisons but for any expression; this means you can write your own functions that "chain" in exactly the same way. I love this aspect of Icon and wish more languages could incorporate goal-directed evaluation.
N.B. In Guido's paper introducing Python at VHLL (middle 1990s) he mentions Icon explicitly as a source of inspiration in the design of Python.
This sounds like a simple request (and clearly it is simple enough that python implemented it) but it is not necessarily that easy to use. It actually opens up the ability for a lot of errors to be caused.
Specifically, any time that you use functions (or properties in the case of C#, Getters for Java)
So
public int GetX()
{
return 4;
}
(2 < GetX() < 5);
(2 < GetX() > 5);
(5 < GetX() < 2);
Seems like it would be really simple. But problems occur if GetX() has side effects.
private int val = 10;
public int GetCountdown()
{
return val--;
}
(2 < GetCountdown() < 5);
(2 < GetCountdown() > 5);
(5 < GetCountdown() < 2);
In this situation, is "GetCountdown()" decremented twice or just once?
Would the "chained-if-statement" ever shortcut?
Consider the last statments, which roughly evaluates (in english) to "Is 5 less than some value which is less than 2) which should be impossible, but depending on the implementation and side effects, it is possible that some function (Random.NextInt()) could pass both of those tests.
So, for that reason, it would be required that each of the items is only evaluated once, the saved into a local variable for the next comparison. But then you get into shortcutting problems.
public int GetOne()
{
return 1;
}
public int GetVar()
{
return -1;
}
(GetOne() < GetVar() < GetDBVal() < GetUserInput())
Generally, you would want to first check constants and variables before doing a database hit. But if we said (as we said earlier) that all the values must be saved into local variables ahead of time, this means that it might be calling a database hit, and asking the user for information even though "GetVar()" is -1, and so the first comparison fails)
As I said earlier, clearly Python allows this syntax, so it is clearly possible. But, regardless of the technical implications which I have laid out (all of which are easy to design around) it means that your code is less clear because the next person who reads it does not know whether or not you have considered all of this. Whereas, if(x > 2 && x < 5) { } seems clear to me, I know what it does, and I know what the coder intends.