Conditional operator as a statement

[JonB]

@SimonSchroeder said in Conditional operator as a statement:

The general rule is to never user ?:, but to use regular if/else instead.

Hi Simon. I always read your posts with interest. To be 100% clear, you are not speaking about using ? : in general in its normal "expression-result" context are you? You have no problem with e.g. variable = b ? x() : y();, do you? Only with using it as a statement, b ? x() : y();, right? Where we are indeed all agreeing this is not a "recommended" construct.

Reading through the C++ standard now I come across two apparently legitimate uses of ? : which are surprising to me at least, and germane to this thread.

First, they spend time discussing what to do when either side of the : is of type void. Which I cannot see as usable in any context where the expression result is used (e.g. assignment to variable or in an if condition). This only makes sense (to me) in statement

cond ? voidFunc() : voidFunc2();

Second, they further comment on the result of the : being potentially an lvalue rather than the typical rvalue one would expect. This only makes sense (to me) in statement

(x ? y : z) = 42;

which perhaps surprisingly is apparently legitimate.

[jsulm]

@JonB said in Conditional operator as a statement:

(x ? y : z) = 42;

Should remember this next time I ask for code review for a C++ commit :-D

[JonB]

@jsulm
Indeed :) I took this from https://en.cppreference.com/w/cpp/language/operator_other.html, at the end of the Conditional operator sub-topic, where they give:

    // simple lvalue example
    int m = 10; 
    (n == m ? n : m) = 7; // n == m is false, so m = 7

! :)

[J.Hilk]

@JonB said in Conditional operator as a statement:

Second, they further comment on the result of the : being potentially an lvalue rather than the typical rvalue one would expect. This only makes sense (to me) in statement

(x ? y : z) = 42;

which perhaps surprisingly is apparently legitimate.

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[JonB]

@J.Hilk
I recognise the code language in your blob! It is "brainf*ck", and I have previously done a bit of coding/playing in it! :) One of the finest, simple languages out there, I don't know why it is not used widely in real world programming ;-)

[J.Hilk]

@JonB turing completeness is all you need.

Everything else is for those nerds that are concerned with silly stuff like compute time or physical limits of memory.

Pfft

[JonB]

@J.Hilk
It's great. Simple, clearly documented, and no undefined behaviour. As a bonus IIRC (unless I am mistaken, haven't checked?) you cannot actually put comments into your code (unless yours work because it ignores any non-language characters?), which is also great for code writing....

[J.Hilk]

@JonB No question about it.

But the perfect programming language is GulfOfMexico (previously known as DreamBerd)

I highly recommend checking it out:

https://github.com/TodePond/GulfOfMexico

[jsulm]

@J.Hilk Brainfuck?

[JonB]

@jsulm

@JonB said in Conditional operator as a statement:

@J.Hilk
I recognise the code language in your blob! It is "brainf*ck",

But I was a bit politer than you in what I typed to leave on a forum.

[Kent-Dorfman]

@Christian-Ehrlicher said in Conditional operator as a statement:

btw: I've a similar statement in python where I sa a c++ programmer always have to thunk about it: a = 3 if b == 4 else 5

Actually I use that python ternary-if statement quite frequently, but as for using a ternary-if as a statement in c++: I would NOT do it in my code as a statement, but only as an evaluated expression, usually assigning the result.

I'm a huge fan of ternary-if, btw! I find myself preferring it in yes/no situations..

[JonB]

@Kent-Dorfman said in Conditional operator as a statement:

python ternary-if statement

It cannot be used as a statement in Python, only as an expression. That's what we are talking about compared to C++'s ? :.

[SimonSchroeder]

@JonB said in Conditional operator as a statement:

You have no problem with e.g. variable = b ? x() : y();, do you? Only with using it as a statement, b ? x() : y();, right?

You are correct, I don't have a problem with variable assignment. (I tried to clarify this by the examples I gave.) Still, I would say the general rule is to not use them. You should only use them when you really need them. Sometimes there is no other language feature that could achieve the same thing, and then it is totally fine. Just don't be too smart about it.

(I'm personally a heavy user of ?:. I have just accidentially found this 'beauty' in my source:

std::ifstream in_winter(type == MIN ? "stats-" + std::to_string(year) + "-winter-min.csv"
                      : type == MAX ? "stats-" + std::to_string(year) + "-winter-max.csv"
                                    : "stats-" + std::to_string(year) + "-winter-mean.csv");

MIN and MAX are enum values.)

[J.Hilk]

@SimonSchroeder said in Conditional operator as a statement:

(I'm personally a heavy user of ?:. I have just accidentially found this 'beauty' in my source:

std::ifstream in_winter(type == MIN ? "stats-" + std::to_string(year) + "-winter-min.csv"
: type == MAX ? "stats-" + std::to_string(year) + "-winter-max.csv"
: "stats-" + std::to_string(year) + "-winter-mean.csv");
MIN and MAX are enum values.)

[JonB]

@SimonSchroeder

std::ifstream in_winter(type == MIN ? "stats-" + std::to_string(year) + "-winter-min.csv"
                      : type == MAX ? "stats-" + std::to_string(year) + "-winter-max.csv"
                                    : "stats-" + std::to_string(year) + "-winter-mean.csv");

I think it's fine you chose ? : here. if else would have been much longer. But just for the record I have a thing about about factoring and not repeating. I would probably have written yours as something like:

var amount = (type == MIN) ? "min" : (type == MAX) ? "max" : "mean";
std::ifstream in_winter("stats-" + std::to_string(year) + "-winter-" + amount + ".csv");

:) To me this makes it clear that the "test" is simply for the word min/max/mean and everything else is the same. And the lines are not too long!

[J.Hilk]

@JonB I would have gone with a lambda function and a full switch case approach. We're dealing with enums after all, and it screams at me: "THIS WILL EXPAND TO MORE FILES!"

[JonB]

@J.Hilk said in Conditional operator as a statement:

lambda function and a full switch case approach

Nah....!! KISS!! :)

And for the record I wouldn't use a switch statement to return a simple value where there are only 2 explicit case and a default. Why write a multiline essay to pick between a couple of literal string values? Of course it's only IMHO, and each to their own....

[J.Hilk]

@JonB I value readability over simplicity for simplicity’s sake..

[JonB]

@J.Hilk I agree.
And personally I find a couple of ? :s, in one line, as more readable than a multiple line switch statement and a lambda. Each to their own :)

[J.Hilk]

@JonB

auto winter_stats_filename = [](int year, Type type) -> std::string {
    const char* suffix = "mean"; // Fallback
    switch (type) {
        case Type::MIN:  suffix = "min";  break;
        case Type::MAX:  suffix = "max";  break;
        case Type::MEAN: suffix = "mean"; break;
        default:
            assert(false && "winter_stats_filename: unexpected Type value");
            break;
    }
    return "stats-" + std::to_string(year) + "-winter-" + std::string(suffix) + ".csv";
};

std::ifstream in_winter(winter_stats_filename(year, type));

I agree, sometimes I have the correct opinion and sometime the others have to wrong opinion :P