Seriously though, there's nothing in ternary operator that says it should only be used for side-effect free code. Especially in C++ (or Java), which doesn't even differentiate between stateless and stateful code on the language level.
IMO ternary is a perfect solution for the case where you want to assign or return a different value based on a boolean condition. Whether or not the code in branches is side-effect free is irrelevant.
Personally, where I try to avoid using ternary operator, is places where I don't care about returned value. So "yes" for:
auto foo = [condition] ? possibly_stateful_then() : possibly_stateful_else();
I agree. If a function isn't side-effect-free, then you've got other problems besides whether it's used with a ternary operator.
My primary language, Object Pascal, even goes to the length of naming functions (return values) and procedures (don't return values) differently. It really helps to focus the mind on the purpose of each: one almost always expects procedures to do something and, most likely, modify something that may introduce side effects. Functions are almost always side-effect-free in "decent" Object Pascal code.
Ternaries are often used as single-usage substitites for a variable, but it's not rare to see the ternary statement simply copied somewhere else if the same value is needed again.
Using ternaries only when it is free of side-effect can both helo avoid a class of unnecessary errors, and add meaningful semantic information that some code is, or should be, side-effect free.
It would be great if the compiler(s) in various languages supported enforcing it, but sometimes you take whatever you get.
No solid reason, just a feeling. I feel that if-else block communicates intent more clearly when you're dealing with statements - because it can't return a value in languages we're discussing, it's specialized for that job. The same motivation makes ternary better when we care about a value.
To be honest, with that explanation the decision you made has nothing to do with ternaries, and is entirely just the mirroring of the decision the if forced on you.
Also,
> in languages we're discussing
Don't bury that lede. If you're restricting what you're saying to a specific language say that bold and as the very first thing, so people don't end up wasting their time parsing your post in a different context. Rude.
> To be honest, with that explanation the decision you made has nothing to do with ternaries, and is entirely just the mirroring of the decision the if forced on you.
I like to think of it as using the dedicated tool for a job it was designed for. In my mind, it's a good rule of thumb because it enhances readability (compare "the principle of least surprise").
> Don't bury that lede. If you're restricting what you're saying to a specific language say that bold and as the very first thing, so people don't end up wasting their time parsing your post in a different context. Rude.
Why? Come on, at this point in the thread we'll still discussing C++ derivatives. I thought it was obvious.
Also: if a lanuguage has an if/else as an expression and has a ternary operator, then IMO there's a problem with that language being cluttered with duplicate syntax for the same thing.
What is your justification for the restriction though?
Personally i dislike the latter form because it requires me to spend extra time reading what is boilerplate that is functionally identical to a ternary.
Edit: Not impressed by the down-voting of an earnest question of someone trying to learn more about how other people see things, HN.
Why are those the only options? I know languages where if/else blocks return values. (Rust, Julia, Python, Perl, R) I also know languages that allow easy ways to embed multi-line blocks into a ternary. (Rust, Perl)
I'm sorry, but i really don't follow your logic, can you try to explain it more clearly?
My comment, and the comments above it are all about C-style languages (C, C++, C#, Java).
Languages with very different syntax like Python are of course going to have different style preferences. Eg. Python doesn't have a ?: operator at all, just an inline if-else expression, so the entire discussion of "should you use ?: for control flow" is meaningless for Python.
Does Rust/Julia/Python/Perl/R feature ternary operators?
The classic languages with ternary (C, C++, Java, PHP, JavaScript) all have the deficiency of distinction between statements and expressions. When everything in your language is an expression, the need for ternary disappears.
In Python the if/else block does not return a value.
Python has a ternary operator, which does return a value. It just so happens this operator uses the tokens `if` and `else`. But it's the same thing what you'd write in C or Javascript as `C ? T : F`, would be written `T if C else F` in Python. Different order of arguments and tokens, but it's still the ternary operator and not an if/else block.
You can't get a result from block statements in Python. Just because the ternary operator uses the same tokens as the if/else block, doesn't mean it's the same thing.
Are you saying this suggests it does something different from what it does? What does it suggest?
boolean_flag
? do_this()
: do_that();
It seems so terse as to be impossible to misinterpret.
The only possibly feasible way i see for it doing something unexpected would be if it were the last statement in a function in a language that implicitly returns the value returned by the last statement in a function; but users of such languages usually are aware that can happen.
Ternaries strongly suggest "side effect-free statement being run for its return value." Perhaps a more apt analogy would be to say it's like writing a method called "getX" with side effects.
As far as i am aware ternaries put no restriction whatsoever on what kind of code you can put in its branches.
I don't buy the comparison with getX either, since ternaries have no name, they're just some punctuation, and even if implemented as if/else word pairs are completely vague.
> As far as i am aware ternaries put no restriction whatsoever on what kind of code you can put in its branches.
You just called someone out for this:
"If you're restricting what you're saying to a specific language say that bold and as the very first thing (...)"
Are you talking about a specific language now? Because some languages do put restrictions on that. Python makes a clear distinction between statements and expressions, so you don't even get the option to use a ternary in place of an if/else block.
That said, (in general) I disagree that ternaries suggest side-effect free. However, they do suggest that you care about the return value of the ternary expression. Some languages enforce this suggestion, others don't. But even for languages that don't, a ternary that silently discards its return value feels like a "cute hack" to me.
It might be a convention in some circles. I don't think it's a well-established one, though.
For me, ternaries strongly suggest "expressions being run for its return value", but without any indication whether or not it's side effect-free. In practice, most of the time such expressions end up being side effect-free (getters, finders, etc.), but every now and then you do want to have a stateful expression (e.g. getting something from a map, and storing a default value there if the key is missing in the map). I believe such stateful expressions are fine to use with ternaries as well.
OK, maybe I don't quite literally mean side effect-free. In that case I probably wouldn't think it's bad. What I would not expect in a ternary statement is code that, say, makes a network request, or writes to disk, or changes several different properties on the current object.
I can't give you a hard reason. I guess when I learned C all examples were like c=yesno?1:2. So I guess I stuck to it and never thought about triggering an action with side effects that way.
So as an example of doing both, consider following Java pseudocode (simples example that comes to my mind now):
Foo value = someCondition()
? map1.computeIfAbsent("key", defaultValueProvider)
: map2.computeIfAbsent("key", defaultValueProvider);
This both gets a value and changes state of the map; which map is queried/altered is determined by the condition. I personally don't mind such code, and prefer it to if/else version.
I have been doing this for a while and I am trying to keep things simple and consistent now. I used to do "elegant" code that used a ton of language features but now my PHP or C# look almost the same.
So: