A staple of compact code, the ternary operator
?: feels like it's earned a place in any programming language. I use it often; you should use it often. However, I don't like the operator itself. It feels complex and incomplete. Though I've stopped development on Leaf, I did find a better option.
Let's take a deeper look at what this ternary operator is, then show how a language could avoid it.
What's this ternary operator?
The name of this operator raises questions. A ternary operator, in a typical math sense, or from the view of a parser, is an operator that takes three arguments. An operator is a function that has a special syntax, not the generic call syntax
foo(a,b,c). Most common are binary operators, we see them everywhere.
//binary operators x + y x / y x * y
There are also a handful of unary operators we see commonly. Unary meaning they have only one argument.
//unary operators -a ~bits !cond
There's no shortage of unary and binary operators. But what examples of ternary operators do we have?
//ternary operators cond ? true_value : false_value
Are you scratching your head trying to think of another one? As far as I know, there aren't any. This is why we end up calling this the "ternary operator" instead of using a proper name, like "conditional operator". There aren't any other ternary operators in programming languages.
Let's step aside for a second. There are operator sequences and combinations that may look like ternary operators but aren't.
For example, this Python comparison appears to involve three arguments.
if a < b < c: go()
That looks similar to a ternary operator. It must consider all three arguments to evaluate correctly.
However, digging deeper this is more of a syntactic sugar than a true ternary operator. It's equivalent to the following.
once_b = b if a < once_b and once_b < c: go()
You may find several examples that show only
a < b and b < c, but those are incorrect. The original form guarantees that
b is evaluated only once. I use the
once_b = b to show this guarantee; I assume a different internal feature achieves this in practice.
This python construct can be extended to include even more values.
if a < b < c < d <e < e: go()
It's a chained operator. There's no limit to what can be added.
<< stream operator in C++ can also be chained.
cout << "Hello " << first_name << " " << last_name << endl;
Unlike Python's chained comparisons, this C++ sequence doesn't require any parser support.
<< is a normal binary operator that happens to be chainable. Basic math has this same property, for example
a + b + c + d.
Messy syntax and parsing
I said there aren't any other ternary operators in programming languages. There's a good reason for this.
cond ? true_value : false_value. Is there anything that makes it look like three arguments are involved? What if I change the operators slightly, to unknown ones:
expr ⋇ value_a ⊸ value_b. That looks like two binary operators. Even if I keep the same symbols, but add nested expressions, it looks off:
cond ? value_a + value_b : value_c * value_d. There's no visual indication that
? ... : is one unified operator. This syntax limitation prevents any new ternary operators from being introduced. It'd create a backlash.
?: is already in some coder's bad books as it's easy to abuse.
Despite providing a valuable syntax, the ternary operator is syntactically messy. It's just weird to have two split symbols define three arguments. A function with three arguments is not a problem since we have a robust syntax for it
foo( a, b, c ).
Adding to the complexity is precedence. All operators require precedence. For example,
a + b * c is evaluated as
a + (b*c). Multiplication has higher precedence than addition. Its result is evaluated before addition.
Operators of the same precedence also have associativity. For example
5 - 2 + 3 is evaluated as
(5 - 2) + 3 = 6, which is left associative. Right associativity would be evaluated as
5 - (2 + 3) = 0, which is wrong.
Right associativity is generally reserved for unary operators, which only have a right argument, and assignment operators. For example, if you're crazy enough to write
a = b += c, right associativity evaluates this as
a = (b += c).
The ternary operator is right associative. It doesn't feel right though. How can an operator with three arguments and two symbols have associativity defined merely as left or right?
cond_a ? val_one : cond_b ? val_two : val_three //right? associative cond_a ? val_one : (cond_b ? val_two : val_three) //left? associative (wrong) (cond_a ? val_one : cond_b) ? val_two : val_three //strict-left? associative (wacky) (((cond_a ? val_one) : cond_b) ? val_two) : val_three //strict-right? associative (nonsensical) cond_a ? (val_one : (cond_b ? (val_two : val_three)))
The two strict forms, which apply associativity on each operator symbol, are wacky. Think for a moment from the point of the view of the parser. It's one of those two that make the most sense syntactically. The first two forms require a bit of trickery to bypass regular associative parsing.
Try to imagine what happens in nested ternary operators:
a ? b ? c : d : e. You won't find nested ternaries often in code. They are too hard to parse mentally.
You find lots of code depending on the quasi-right associativity. That's what allows chaining.
int a = cond_a ? val_one : cond_b ? val_two : cond_c ? val_three : val_four;
A binary solution
When I was working on Leaf, I wanted to avoid the ternary operator. I liked the feature it provided, but I wanted to find a more fundamental approach to providing it.
The solution came in the form of language optionals. These were fundamental in Leaf, thus had operator support.
The first operator was a defaulting one. If the optional value were set, it'd evaluate to that. Otherwise, it'd evaluate to the provided default.
var a : optional print( a | 1 ) //prints 1, since `a` has no value var b : optional = 2 print( b | 3 ) //prints 2, since that's the value in `b`
?? that uses
null in the same way as Leaf uses unset optionals.
This sounds like half of what the ternary operator does. We could look at like this:
cond ? some_val | default_val. That is, consider the entire left part, the
cond ? some_val to produce an optional value. Given an optional, we already have operators to default that value when unset.
Leaf incorporated the
? operator to create an optional.
var a = true ? 5 //a is an optional set to value 5 var b = false ? 6 //b is an optional without a value
On its own, this operator is often useful for optionals. Combined with
| default operator it mimics the traditional ternary operator.
var a = cond ? true_value | false_value
int a = cond ? true_value : false_value;
| are both binary operators. There is no need to have an actual ternary operator to produce the same conditional evaluation. We get the same feature without the syntactic messiness. It's a lot clearer what happens, and the parser doesn't require any trickery.
It also improves expressiveness without introducing more symbols, as both operators are useful on their own.
Alas, I've not seen any plans to add this to any language. If you know of one, please leave a comment. I'd be curious to see it.
Top comments (60)
I do love the ternary operator. I can see how others get confused though. In an application where everything is written one way (regardless of the way) and another way is introduced, it will add confusion.
Though if your application's style guide enforces the use of the ternary operator, it becomes idiomatic.
The key to being idiomatic is is consistency. This can be made true even with a nested ternary!
To me, that style with the ternary is a little frustrating because it feels like it's so close to someone embracing a more functional style. It's not that ternary can't exist or be useful in that case, but it just seems like a tease at that point. Like, to take your example and convert it into an admittedly contrived example, it might look something like:
LOL I feel the exact same way. The Ternary feels like an in-between. Somewhere in the middle of imperative and functional.
Today I was actually working on a style guide for a project I'm working on. It looks exactly like the code you created.
It's not quite ready for human consumption, but I think you would find it interesting. Hit me up on Twitter if interested in a sneak peek.
The problem with this is that both
noOrderCountTextwill be evaluated in either case.
Do they have to be functions?
only one function will execute in this case, either the
ifcase or the
elsecase, but never both.
In my version of
ifElse, they can be values that will be returned or functions to be executed.
Yeah, whereas in
condition ? expensiveGet() + 1 : expensiveGet2() - 1only one expression will be evaluated.
Check out Sanctuary's
ifElsesanctuary.js.org. You can live edit their page to see how it works.
I'd love to get some live editing docs page for my stuff too. Pretty neat site.
I see it's actually for threading through the value, just like
However, for normal conditional use it's error prone, as you've shown in your code. Both expensive gets will run before the condition is even applied to true.
The actual code would be
ifElseaccepts functions. So those functions are only executed when the condition is met.
This is still false. Only one will run. Never both.
You can see
logOddis never called.
In your first example
Yes you are correct. The expensiveGet method needs to take 2 arguments for it to work the way it is being called in
I have created a working example that you can run.
This example will show that
ifElseonly executes one of the functions.
I agree with with all your points.
But I feel like there's situations where it's arguably clearer than the alternative.
Other commenters have mentioned the functional angle, and that's really it. In many (all?) the languages that have the ternary operator
ifis a statement (rather than an expression). Make
ifan expression and ternary has no place in the world:
Note, I say we don't need the ternary because it can be replaced with general purpose binary operators. I'm not suggesting to get rid of the functionality, that'd be crazy-talk.
I've found one good use for the ternary operator: clearly and succinctly transforming a callback into a promise:
But even still, the ternary operator does not pass the Crockford test.
You could still do that without the ternary and in the same space:
No, just... no.
The ternary operator is better than logical operator abuse.
how is making a binary decision operator abuse?
Because what you actually want is an if-then-else path. The ternary operator has been conceived for that. Logical operators are for logical expression.
Sure you can use them to create conditional branching, but that doesn't make that any clearer. It's hiding the broken glass under the rug (i.e., not using the ternary operator for the sake of not using it, not because you're opting for a clearer pattern).
Fair enough regarding clarity, though in that case we could say that the given example is at fault and not how we decide to return the result ;). It's true that rather than check if error is truthy, it'd be nicer to write something like
reject(error) || resolve(data). (I know that doesn't make sense for promise resolution, but bear with me as it's just the example we're working with.)
Regarding "logical operators are for logical expression", the ternary operator's left hand side expression is already a logical expression by nature. Adding a syntax for deciding whether to go "left or right" that doesn't follow the same rules as any other operator in the language and worse, different from the ternary implementations in other, older languages can add confusion where there doesn't need to be.
All that aside, I love the ternary operator when writing, but during reviews, or walking people through later, what seemed so simple to me at the time of writing is rarely as clear. The logical or's result is immediately clear.
A pattern I also see (specifically in new React developers, I think) is returning null as the right hand operand for the ternary. I think it's a weird case of "the ternary operator is cool and I want my code to be concise". That added layer of "need to actually learn the ternary operator to write it" creates a desire to use and abuse it.
Edit, for clarity and stuff: As with everything in programming there's a time and place for everything. But if your goal is to have a single line, immediate "true or false" result of something, I feel the logical or is made for that. There's a small window where the ternary probably doesn't hurt anything but is ultimately the same as using multiple logical ors. Anything much larger or nested probably calls for actual if/else.
I like the ternary. Like @fnh pointed out, it's the only way of doing direct conditional assignment in most languages. And for the most part, we've conditioned ourselves to how it works.
But I have a hard rule: never nest a ternary. No matter how clever it makes me seem, or how many articles I read on functional programming and why ternaries are awesome, I won't. The stress it puts other programmers (and myself!) through to mentally parse a nested ternary isn't worth it.
Yes, nesting of the second argument, the truth value, can be hideous. Nesting, or better called chaining, of the third argument can be acceptable with good formatting.
You basically just replaced
condition ? if_true : if_falsewith
condition && if_true || if_false- that means that a falsy
if_truewill fall through to
I don't really see the advantage of that solution.
No, because I'm not allowing "falsey" conditions, which I consider a failure in a language.
falseis a distinct value from an unset optional, and
trueis not the same as an optional with a value.
Having hard optional semantics allows this to work. Using truthy and falsey evaluations this fails.
A condition can obviously be false, but I guess that's not what you meant. For the sake of this argument, let's assume that condition
cis true, value
1; in most languages,
c ? x : ywould result in
c && x || ywould result in
If I understood you correctly,
c ? false | 1in leaf would too result in
1, thus breaking the original logic of a ternary operator.
c ? false | 1would evaluate to
falsein Leaf. The
|operator applies only to optional types, not truthy values.
As I was reading it, I was just thinking about how messed up programming is.
I personally hate the ternary operator. It's a conditional disguised as an assignment and when I scan code, I often read it wrong. So, we removed it from all our code and created an inspection to make sure it never gets back in.
Totally personal preference here, but an if else is much more readable.
I never even considered all the edge cases you brought up or that it works differently in different languages. Do other programming language developers secretly hate programmers (only half kidding)?
@Blaine I like to think of all the various programming languages as exactly that, languages. Imagine if you will, that C is latin. Its the root of most modern "western" languages (for brevity sake). Each language that sprouts from it has syntax that is similar but more refined and easier to use in particular circumstances that are important to that language. Then within that language itself there are deeper refinements, these are the regional dialects. It's actually quite interesting.
Yes, I'm aware. The research shows that C-like language syntax is basically as hard to learn as random syntax. That's not good. It makes programming harder than it needs to be. And every time I see some crazy-dense and indecipherable code I wonder what we're really doing here. Are we trying to be cryptographers, jerks, or what?
Programming is already cognitively demanding. We should be saving or brain cycles for our programs, not trying to remember all the obscure edge cases of the ternary operator in C.
If...Else statements are flow though. I don't like using them in situations where I'm alternating between expression values. I let the high-level logic usually decide whether I want an if-else or a conditional-operator. If I use the wrong one it will look odd.
That's a fair point. In my code base, the previous programmers used them indiscriminately, which was part of the reason we're got rid of them. I've seen that pattern of usage in open source projects too.
If you used them consistently in the manor you've described, I could get on board with it.
I think the ternary is mostly a symptom of the design decision to distinguish between expressions and statements, which many programming languages share. When you could just assign the value of an if or switch/case, as it is the case for example in Ruby, there would be much less need for a ternary operator and especally to nested tenarys.
When you considered the optional type for Leaf, did you have a type that abides the definition for monadic types in mind (e.g. something like the Maybe type in Haskell), to handle null values more gracefully, or was it more a construct for the sake of a simpler grammar?
I had an optional type, which is what these operations were based on. Optional was an essential part of the language, as nothing was allowed to not contain a value otherwise: all defaults were defined, and there weren't null pointers.
IMO (in JS at least), binary operator use for non-binary are good if you know what you're dealing with.
I took care to write "falsy" and "truthy" because:
Yes, but empty array
But you should never care about the number of lines you write. Ninja coder can write this methods in 1 lines ? Whatever, I'll use 10 lines and have a clear code-base.
(condition && b) || c, if
conditionwere true and
bwere false (or zero), it would return
c. So that's not a correct implementation of a ternary operator.
Indeed, that's part of my point. You can do without ternary with some trickery, but best solution is to split it into real
if elseover multiple lines.
Noted that this is already commented elsewhere, but your binary conditional operator seems a lot like this logic operator abuse in JS:
And whenever I see the former I rewrite it as the latter (because it is more semantic, not because I am obsessed with removing 2 characters)
(Also, a falsy
negativeto be evaluated and returned)
A lot of the same issues you point out could also apply to
ifstatements in general, not just the ternary operator. It's an interesting thought, because in other languages there are alternatives to using if statements. SmallTalk booleans were objects which exposed the messages
ifFalse, rather than requiring a special
ifstatement. The FP equivalent would be pattern matching, which maps data patterns to functions/values. Assembly has conditional jumps. All of these are conceptually similar in usage -- run this code when this condition is present.
Could it be that the deeper problem here is the
ifstatement itself? (Since ternary is just an expression + operator form of this.) This is an honest question for discussion, since I use
ifat times and it is considered a staple programming construct.
ifstatements are something separate, assuming the ternary isn't being abused to introduce logic flow into a program.
ifstatements are about flow, adn there's simply no way to get rid of them. Sure, in many cases we have higher level things, like select, or even dynamic dispatch, but the essential conditional logic persists.
Most languages use
iffor flow control so they encourage you to write boolean reductions for your data and to think of your decisions in terms of booleans. Whereas my human brain doesn't tend to actually think in Discrete Logic. Sometimes I even draw truth tables to make sure it will produce the expected result. The problem isn't really with the language feature provided by
if, but perhaps with our overuse of the construct.
So I guess the fundamental question is: does using
ifreduce the expressiveness of your solution? And if so, what are the alternatives?
When I am writing a guard clause,
if's expressiveness is probably fine. But when I am making business decisions, using
iffor flow can feel pretty bad at times. As far as the 2nd question, I think really the only alternative to using
ifis to write higher level code so it is not needed. Those implementations will vary based on the problem and paradigm. Examples I've used: union types or shallow inheritance to make discrete data states.
As far as the relationship, ternary is just an expression + operator version of
if. Being an operator makes it more cryptic, but I consider it being an expression to be a good thing. I tend to write in expression-based languages, so in my mind it is the exact same capability as
if. (In F#,
ifis an expression and no ternary operator exists.) From that perspective, putting "too much" in the ternary operator feels appropriately bad because it is highlighting problems with expressing solutions in terms of booleans. Whereas the same code with a statement-based
ifmay feel more comfortable than it should. Not that I am in favor of ternary. I think your alternative is better. I guess I was just isolating a problem that most people easily identify with ternary, but is less obvious with if. That being the lack of human legibility of boolean-based flow control.
This is exactly why I like Python's ternary operator:
The use of English words instead of cryptic symbols reduces the ambiguity.
Python's ordering is backwards. IT breaks the standard if-then logic and chooses then-if wording. I really dislike the Python way of handling this.
That's interesting, I tend to think about conditionals the same way it is in Python, ie "do this thing if something is true otherwise do this other thing", rather than "if something is true do this thing otherwise do this other thing".
It's interesting how different people think differently. :)
First, pretty well all of the Lisp family have a ternary operator ... the 'if' expression. The observation that the true/false branch operatoronly exists in languages with if-statements is apposite. The people at Bell Labs were mathematicians, and probably felt quite comfortable with the idea of expressions with conditional paths. I am fairly sure that that is their intended purpose.
It is easy to write inscrutable code in any language, and many of the examples of cryptic conditionals we encounter are cryptic because they aren't adequately described.
Knuth's whole aim with 'literate programming' was to make everything clear, and if he can make chunks of raw TeX understandable to a novice (he does), then we can certainly make our conditional expressions intelligible.
It is true that we don't NEED the operator, but why do we NEED anything more that machine code? ... It is because, correctly used, these languages and their constructs make things clearer.
... And part of that 'correctly' is adequate commenting.
Oh, I definitely think we need the functionality. I think part of my intent of the article didn't come across. I mean we don't need a ternary operator because we could instead define two binary operators which are more generic, and also fulfill the conditional evaluation expression.
My concern about parsing is strictly due to the ternary syntax. Once we have binary operators it can be parsed, by machine and humans, the same way as other binaries and thus be even easier to understand.
It could be that calling it an operator is simply confusing.
Coffeescript has a
Which makes it look more like an inline if that returns its values from the
So, the conditional operator would be more like:
I really like the solution though, it makes so much more sense to have it be made up of binary operators now. It doesn't even make sense to add the conditional operator back in since the
|are already fully encompassing its use cases.
I really dislike the inline
if ... elseforms that some languages have, also including Python. It looks really messy, and more like a flow statement than an expression.
As usual, the Adaist is different :-)
Ada (since 2005, I guess) has a "kind of" ternary operator that has some similarity with Ruby. In Ada you use just a "if" construct
X := (if (a > b) then 4 else 5);
If I am not wrong (I am to lazy to start the IDE and try...) you need the parenthesis around the if. I did not check thoroughly, but I think that this prevent the issues with associativity: "if" expressions have no associativity and you need parenthesis to use them. (Ada also force you to use parenthesis in expressions with both "and" and "or," in order to avoid ambiguities).
The nice part is that there is also a "case" expression
X := case day is
when Monday => 3,
When Sunday => 4,
They are very convenient, especially in inline functions.
Speaking of python, there are conditional expressions docs.python.org/2.5/whatsnew/pep-3...
which is, I think, the only valid use case for ternaries: providing initial values based on a condition.
Apart from that a simple if clause to return early does the trick. No need for nesting ternaries.