I have some kind of an ideological question, so:
Suppose I have some templated function
template <typename Stream>
void Foo(Stream& stream, Object& object) { ... }
which does something with this object and the stream (for example, serializes that object to the stream or something like that).
Let's say I also add some plain wrappers like (and let's say the number of these wrappers equals 2 or 3):
void FooToFile(const std::string& filename, Object& object)
{
std::ifstream stream(filename.c_str());
Foo(stream, object);
}
So, my question is:
Where in this case (ideologically) should I throw the exception if my stream is bad? Should I do this in each wrapper or just move that check to my Foo, so that it's body would look like
if (!foo.good()) throw (something);
// Perform ordinary actions
I understand that this may be not the most important part of coding and these solutions are actually equal, but I just wan't to know "the proper" way to implement this.
Thank you.
In this case it's better to throw it in the lower-level Foo function so that you don't have to copy the validation and exception throwing code in all of your wrappers. In general using exceptions correctly can make your code a lot cleaner by removing a lot of data validation checking that you might otherwise do redundantly at multiple levels in the call stack.
I would prefer not to delay notifying an error. If you know after you have created the stream, that it is no good, why call a method that works on it? I know that to reduce code-redundancy you plan to move it further down. But the downside of that approach is a less-specific error message. So this depends to some extent on the source-code context. If you could get away with a generic error message at the lower-function level you can add the code there, this will surely ease maintanence of the code especially when there are new developers on the team. If you need a specific error message better handle it at the point of failure itself.
To avoid code redundancy call a common function that makes this exception/error for you. Do not copy/paste the code in every wrapper.
The sooner you catch the exceptiont the better. The more specific the exception is - the better. Don't be scared of including most of your code into a try catch blocks, apart fromt he declaration.
For example:
int count = 0;
bool isTrue = false;
MyCustomerObject someObject = null;
try
{
// Initialise count, isTrue, someObject. Process.
}
catch(SpecificException e)
{
// Handle and throw up the stack. You don't want to lose the exception.
}
I like to use helper functions for this:
struct StreamException : std::runtime_error
{
StreamException(const std::string& s) : std::runtime_error(s) { }
virtual ~StreamException() throw() { }
};
void EnsureStreamIsGood(const std::ios& s)
{
if (!s.good()) { throw StreamException(); }
}
void EnsureStreamNotFail(const std::ios& s)
{
if (s.fail()) { throw StreamException(); }
}
I test them immediately before and after performing stream operations if I don't expect a failure.
Traditionally in C++, stream operations don't throw exceptions. This is partly for historic reasons, and partly because streaming failures are expected errors. The way C++ standard stream classes deal with this is to set a flag on a stream to indicate an error has occurred, which user code can check. Not using exceptions makes resumption (which is often required for streaming ops) easier than if exceptions were thrown.
Related
I have a class which is loaded from an external file, so ideally I would want its constructor to load from a given path if the load fails, I will want to throw an error if the file is not found/not readable (Throwing errors from constructors is not a horrible idea, see ISO's FAQ).
There is a problem with this though, I want to handle errors myself in some controlled manner, and I want to do that immediately, so I need to put a try-catch statement around the constructor for this object ... and if I do that, the object is not declared outside the try statement, i.e.:
//in my_class.hpp
class my_class
{
...
public:
my_class(string path);//Throws file not found, or other error error
...
};
//anywhere my_class is needed
try
{
my_class my_object(string);
}
catch(/*Whatever error I am interesetd in*/)
{
//error handling
}
//Problem... now my_object doesn't exist anymore
I have tried a number of ways of getting around it, but I don't really like any of them:
Firstly, I could use a pointer to my_class instead of the class itself:
my_class* my_pointer;
try
{
my_class my_pointer = new my_class(string);
}
catch(/*Whatever error I am interesetd in*/)
{
//error handling
}
The problem is that the instance of this object doesn't always end up in the same object which created it, so deleting all pointers correctly would be easy to do wrong, and besides, I personally think it is ugly to have some objects be pointers to objects, and have most others be "regular objects".
Secondly, I could use a vector with only one element in much the same way:
std::vector<my_class> single_vector;
try
{
single_vector.push_back(my_class(string));
single_vector.shrink_to_fit();
}
catch(/*Whatever error I am interesetd in*/)
{
//error handling
}
I don't like the idea of having a lot of single-element vectors though.
Thirdly, I can create an empty faux constructor and use another loading function, i.e.
//in my_class.hpp
class my_class
{
...
public:
my_class() {}// Faux constructor which does nothing
void load(string path);//All the code in the constructor has been moved here
...
};
//anywhere my_class is needed
my_class my_object
try
{
my_object.load(path);
}
catch(/*Whatever error I am interesetd in*/)
{
//error handling
}
This works, but largely defeats the purpose of having a constructor, so I don't really like this either.
So my question is, which of these methods for constructing an object, which may throw errors in the constructor, is the best (or least bad)? and are there better ways of doing this?
Edit: Why don't you just use the object within the try-statement
Because the object may need to be created as the program is first started, and stopped much later. In the most extreme case (which I do actually need in this case also) that would essentially be:
int main()
{
try
{
//... things which might fail
//A few hundred lines of code
}
catch(/*whaveter*/)
{
}
}
I think this makes my code hard to read since the catch statement will be very far from where things actually went wrong.
One possibility is to wrap the construction and error handling in a function, returning the constructed object. Example :
#include <string>
class my_class {
public:
my_class(std::string path);
};
my_class make_my_object(std::string path)
{
try {
return {std::move(path)};
}
catch(...) {
// Handle however you want
}
}
int main()
{
auto my_object = make_my_object("this path doesn't exist");
}
But beware that the example is incomplete because it isn't clear what you intend to do when construction fails. The catch block has to either return something, throw or terminate.
If you could return a different instance, one with a "bad" or "default" state, you could have just initialized your instance to that state in my_class(std::string path) when it was determined the path is invalid. So in that case, the try/catch block is not needed.
If you rethrow the exception, then there is no point in catching it in the first place. In that case, the try/catch block is also not needed, unless you want to do a bit of extra work, like logging.
If you want to terminate, you can just let the exception go uncaught. Again, in that case, the try/catch block is not needed.
The real solution here is probably to not use a try/catch block at all, unless there is actually error handling you can do that shouldn't be implemented as part of my_class which isn't made apparent in the question (maybe a fallback path?).
and if I do that, the object is not declared outside the try statement
I have tried a number of ways of getting around it
That doesn't need to be a problem. There's not necessarily need to get around it. Simply use the object within the try statement.
If you really cannot have the try block around the entire lifetime, then this is a use case for std::optional:
std::optional<my_class> maybe_my_object;
try {
maybe_my_object.emplace(string);
} catch(...) {}
The problem is that the instance of this object doesn't always end up in the same object which created it, so deleting all pointers correctly would be easy to do wrong,
A pointer returned by new is correct to delete. In the error case, simply set the pointer to null and there would be no problem. That said, use a smart pointer instead for dynamic allocation, if you were to use this approach.
single_vector.push_back(my_class(string));
single_vector.shrink_to_fit();
Don't push and shrink when you know the number of objects that are going to be in the vector. Use reserve instead if you were to use this approach.
The object creation can fail because a resource is unavailable. It's not the creation which fails; it is a prerequisite which is not fulfilled.
Consequently, separate these two concerns: First obtain all resources and then, if that succeeded, create the object with these resources and use it. The object creation as such in this design cannot fail, the constructor is nothrow; it is trivial boilerplate code (copy data etc.). If, on the other hand, resource acquisition failed, object creation and object use are both skipped: Your problem with existing but unusable objects is gone.
Responding to your edit about try/catch comprising the entire program: Exceptions as error indicators are better suited for things which are done in many places at various times in a program because they guarantee error handling (by default through an abort) while separating it from the normal control flow. This is impossible to do with classic return value examination, which leaves us with a choice between unreadable or unreliable programs.
But if you have long-lived objects which are created only rarely (in your example: only at startup) you don't need exceptions. As you said, constructor exceptions guarantee that only properly initialized objects can be used. But if such an object is only created at startup this danger is low. You check for success one way or another and exit the program which cannot perform its purpose if the initial resource acquisition failed. This way the error is handled where it occurred. Even in less extreme cases (e.g. when an object is created at the beginning of a large function other than main) this may be the simpler solution.
In code, my suggestion looks like this:
struct T2;
struct myEx { myEx(const char *); };
void exit(int);
T1 *acquireResource1(); // e.g. read file
T2 *acquireResource2(); // e.g. connect to db
void log(const char *what);
class ObjT
{
public:
struct RsrcT
{
T1 *mT1;
T2 *mT2;
operator bool() { return mT1 && mT2; }
};
ObjT(const RsrcT& res) noexcept
{
// initialize from file data etc.
}
// more member functions using data from file and db
};
int main()
{
ObjT::RsrcT rsrc = { acquireResource1(), acquireResource2() };
if(!rsrc)
{
log("bummer");
exit(1);
}
///////////////////////////////////////////////////
// all resources are available. "Real" code starts here.
///////////////////////////////////////////////////
ObjT obj(rsrc);
// 1000 lines of code using obj
}
I am currently building an embedded system and use a modern C++ compiler.
While I could technically fit exception handling in the given resources (ARM7, more than 10M RAM), I don’t think exceptions are the right tool for something like this and using exceptions requires RTTI, which in turn results in code bloat.
To stay C++-ish anyway I want to use std::error_code (or similar with more data) because I do like the concept.
However, there does not seem to be any consenus on how to actually use them. I have seen at least four different ways of passing them between function calls, two of them with multiple semantics.
Passing by pointer as an argument
void somefunction(Args..., std::error_code* error);
This is the way I have not seen that often and the one I dislike the most. It leaves the return type fully available and (often, but not always) passing nullptr resulted in normal throwing behaviour.
Passing by reference as an argument
void somefunction(Args..., std::error_code& error);
This is the one I prefer. It leaves returnvalue fully available and makes clear that the error_code is not optional.
Returning it by value
std::error_code somefunction(Ret& out <= if used, Args...);
I have seen this one quite often but don’t really like it that much, as it uses up your return value and I generally don’t like “out parameters” unless there’s no way around them.
Returning a std::variant<Ret, std::error_code>
std::variant<Ret, std::error_code> somefunction(Args...);
This one allows for a return value, but makes accessing both value and error harder. Also, it makes code calling the function more verbose.
Semantics
I have seen both way 1 and 2 with different semantics, if the error_code is passed.
Clear at start and set on error
Only set on error
Return right at start if the error_code is “set”
The last way is pretty good if you want to reduce error checking in the calling code. As you can just pass one error_code to multiple functions without checking in between and everything after the first error will not execute, similar to how exceptions would do it.
I personally do prefer way 2 with checking and returning, however I might be biased.
Is there some recommended / generally accepted way to do it?
Ok, this is no complete answer and actually not perfectly on topic because I am not aware of a standard way to do this. But I once saw a nifty little trick to make error codes harder to misuse. Consider the following code:
struct MyEC {
MyEC() {}
MyEC(MyEC && other) : parent(&other) {
// Maybe log and or abort if other is not checked
other.checked = false;
}
// Delete other constructors and assignment operators
~MyEC() {
if(!checked && parent == nullptr) {
// log and or abort
}
}
[[nodiscard]] std::error_code check() {
checked = true;
return ec;
}
void set(std::error_code err) {
if(parent == nullptr) ec = err;
else parent->set(err);
}
private:
MyEC* parent = nullptr;
checked = true;
std::error_code ec {};
};
int foo(MyEC&& err) {
err.set(/* some error */);
return 5;
}
int foo1(MyEC&&) {
return 4;
}
void bar() {
MyEC err;
foo(std::move(err));
// err has the error code and if its not checked, we will know
foo1(std::move(err));
// even though no error occurs, we will abort if err is not checked.
}
It will even then abort, when the error code is not set but also not checked, which is pretty nice. It has a lot of uses after move, which is a bit weird, but this is no problem here.
In go a common way to do error handling and still return a value is to use tuples.
I was wondering if doing the same in C++ using std::tie would be a good idea when exceptions are not applicable.
like
std::tie(errorcode, data) = loadData();
if(errorcode)
...//error handling
Are there any downsides to doing so (performance or otherwise)? I suppose with return value optimization it doesn't really make a difference but maybe I'm wrong.
One potential problematic case that I could see is the use in a cross-compiler API but that's not specific to this use.
The current way I do this is
errorcode = loadData(&data);
if(errorcode)
...//error handling
but that allows to pass in a value for data.
The errorcode itself is something that is already defined and that I can't change.
Edit: I'm using/have to use C++11
Sometimes output parameters are very handy. Suppose that loadData returns std::vector<T> and is called in a loop:
std::pair<ErrorCode, std::vector<T>> loadData();
for (...) {
ErrorCode errorcode;
std::vector<T> data;
std::tie(errorcode, data) = loadData();
}
In this case loadData will have to allocate memory on each iteration. However, if you pass data as the output parameter, previously allocated space can be reused:
ErrorCode loadData(std::vector<T>&);
std::vector<T> data;
for (...) {
ErrorCode errorcode = loadData(data);
}
If the above is of no concern, then you might want to take a look at expected<T, E>. It represents either
a value of type T, the expected value type; or
a value of type E, an error type used when an unexpected outcome occurred.
With expected, loadData() signature might look like:
expected<Data, ErrorCode> loadData();
C++11 implementation is available: https://github.com/TartanLlama/expected
There are multiple competing strategies for error handling. I will not go into it, as it is beyond the scope of the question, but error handling by return error codes is only one option. Consider alternatives like std::optional or exceptions, which are both common in C++, but not in Go.
If you have a function that is intended to return a Go-style error code plus value, then your std::tie solution is perfectly fine in C++11 or C+14, although in C++17, you would prefer structured bindings instead.
Are there any downsides to doing so (performance or otherwise)?
Yes. With tie, a copy or move of the returned values is required that would not be required if you avoid tie:
auto result = loadData();
if (std::get<0>(result))
...//error handling
Of course, if you would later copy or move the data somewhere else anyway, like in
data = std::move(std::get<1>(result));
then use tie because it is shorter.
So I ran across this (IMHO) very nice idea of using a composite structure of a return value and an exception - Expected<T>. It overcomes many shortcomings of the traditional methods of error handling (exceptions, error codes).
See the Andrei Alexandrescu's talk (Systematic Error Handling in C++) and its slides.
The exceptions and error codes have basically the same usage scenarios with functions that return something and the ones that don't. Expected<T>, on the other hand, seems to be targeted only at functions that return values.
So, my questions are:
Have any of you tried Expected<T> in practice?
How would you apply this idiom to functions returning nothing (that is, void functions)?
Update:
I guess I should clarify my question. The Expected<void> specialization makes sense, but I'm more interested in how it would be used - the consistent usage idiom. The implementation itself is secondary (and easy).
For example, Alexandrescu gives this example (a bit edited):
string s = readline();
auto x = parseInt(s).get(); // throw on error
auto y = parseInt(s); // won’t throw
if (!y.valid()) {
// ...
}
This code is "clean" in a way that it just flows naturally. We need the value - we get it. However, with expected<void> one would have to capture the returned variable and perform some operation on it (like .throwIfError() or something), which is not as elegant. And obviously, .get() doesn't make sense with void.
So, what would your code look like if you had another function, say toUpper(s), which modifies the string in-place and has no return value?
Have any of you tried Expected; in practice?
It's quite natural, I used it even before I saw this talk.
How would you apply this idiom to functions returning nothing (that is, void functions)?
The form presented in the slides has some subtle implications:
The exception is bound to the value.
It's ok to handle the exception as you wish.
If the value ignored for some reasons, the exception is suppressed.
This does not hold if you have expected<void>, because since nobody is interested in the void value the exception is always ignored. I would force this as I would force reading from expected<T> in Alexandrescus class, with assertions and an explicit suppress member function. Rethrowing the exception from the destructor is not allowed for good reasons, so it has to be done with assertions.
template <typename T> struct expected;
#ifdef NDEBUG // no asserts
template <> class expected<void> {
std::exception_ptr spam;
public:
template <typename E>
expected(E const& e) : spam(std::make_exception_ptr(e)) {}
expected(expected&& o) : spam(std::move(o.spam)) {}
expected() : spam() {}
bool valid() const { return !spam; }
void get() const { if (!valid()) std::rethrow_exception(spam); }
void suppress() {}
};
#else // with asserts, check if return value is checked
// if all assertions do succeed, the other code is also correct
// note: do NOT write "assert(expected.valid());"
template <> class expected<void> {
std::exception_ptr spam;
mutable std::atomic_bool read; // threadsafe
public:
template <typename E>
expected(E const& e) : spam(std::make_exception_ptr(e)), read(false) {}
expected(expected&& o) : spam(std::move(o.spam)), read(o.read.load()) {}
expected() : spam(), read(false) {}
bool valid() const { read=true; return !spam; }
void get() const { if (!valid()) std::rethrow_exception(spam); }
void suppress() { read=true; }
~expected() { assert(read); }
};
#endif
expected<void> calculate(int i)
{
if (!i) return std::invalid_argument("i must be non-null");
return {};
}
int main()
{
calculate(0).suppress(); // suppressing must be explicit
if (!calculate(1).valid())
return 1;
calculate(5); // assert fails
}
Even though it might appear new for someone focused solely on C-ish languages, to those of us who had a taste of languages supporting sum-types, it's not.
For example, in Haskell you have:
data Maybe a = Nothing | Just a
data Either a b = Left a | Right b
Where the | reads or and the first element (Nothing, Just, Left, Right) is just a "tag". Essentially sum-types are just discriminating unions.
Here, you would have Expected<T> be something like: Either T Exception with a specialization for Expected<void> which is akin to Maybe Exception.
Like Matthieu M. said, this is something relatively new to C++, but nothing new for many functional languages.
I would like to add my 2 cents here: part of the difficulties and differences are can be found, in my opinion, in the "procedural vs. functional" approach. And I would like to use Scala (because I am familiar both with Scala and C++, and I feel it has a facility (Option) which is closer to Expected<T>) to illustrate this distinction.
In Scala you have Option[T], which is either Some(t) or None.
In particular, it is also possible to have Option[Unit], which is morally equivalent to Expected<void>.
In Scala, the usage pattern is very similar and built around 2 functions: isDefined() and get(). But it also have a "map()" function.
I like to think of "map" as the functional equivalent of "isDefined + get":
if (opt.isDefined)
opt.get.doSomething
becomes
val res = opt.map(t => t.doSomething)
"propagating" the option to the result
I think that here, in this functional style of using and composing options, lies the answer to your question:
So, what would your code look like if you had another function, say toUpper(s), which modifies the string in-place and has no return value?
Personally, I would NOT modify the string in place, or at least I will not return nothing. I see Expected<T> as a "functional" concept, that need a functional pattern to work well: toUpper(s) would need to either return a new string, or return itself after modification:
auto s = toUpper(s);
s.get(); ...
or, with a Scala-like map
val finalS = toUpper(s).map(upperS => upperS.someOtherManipulation)
if you don't want to follow a functional route, you can just use isDefined/valid and write your code in a more procedural way:
auto s = toUpper(s);
if (s.valid())
....
If you follow this route (maybe because you need to), there is a "void vs. unit" point to make: historically, void was not considered a type, but "no type" (void foo() was considered alike a Pascal procedure). Unit (as used in functional languages) is more seen as a type meaning "a computation". So returning a Option[Unit] does make more sense, being see as "a computation that optionally did something". And in Expected<void>, void assumes a similar meaning: a computation that, when it does work as intended (where there are no exceptional cases), just ends (returning nothing). At least, IMO!
So, using Expected or Option[Unit] could be seen as computations that maybe produced a result, or maybe not. Chaining them will prove it difficult:
auto c1 = doSomething(s); //do something on s, either succeed or fail
if (c1.valid()) {
auto c2 = doSomethingElse(s); //do something on s, either succeed or fail
if (c2.valid()) {
...
Not very clean.
Map in Scala makes it a little bit cleaner
doSomething(s) //do something on s, either succeed or fail
.map(_ => doSomethingElse(s) //do something on s, either succeed or fail
.map(_ => ...)
Which is better, but still far from ideal. Here, the Maybe monad clearly wins... but that's another story..
I've been pondering the same question since I've watched this video. And so far I didn't find any convincing argument for having Expected, for me it looks ridiculous and against clarity&cleanness. I have come up with the following so far:
Expected is good since it has either value or exceptions, we not forced to use try{}catch() for every function which is throwable. So use it for every throwing function which has return value
Every function that doesn't throw should be marked with noexcept. Every.
Every function that returns nothing and not marked as noexcept should be wrapped by try{}catch{}
If those statements hold then we have self-documented easy to use interfaces with only one drawback: we don't know what exceptions could be thrown without peeking into implementation details.
Expected impose some overheads to the code since if you have some exception in the guts of your class implementation(e.g. deep inside private methods) then you should catch it in your interface method and return Expected. While I think it is quite tolerable for the methods which have a notion for returning something I believe it brings mess and clutter to the methods which by design have no return value. Besides for me it is quite unnatural to return thing from something that is not supposed to return anything.
It should be handled with compiler diagnostics. Many compilers already emit warning diagnostics based on expected usages of certain standard library constructs. They should issue a warning for ignoring an expected<void>.
I have a setup that looks like this.
class Checker
{ // member data
Results m_results; // see below
public:
bool Check();
private:
bool Check1();
bool Check2();
// .. so on
};
Checker is a class that performs lengthy check computations for engineering analysis. Each type of check has a resultant double that the checker stores. (see below)
bool Checker::Check()
{ // initilisations etc.
Check1();
Check2();
// ... so on
}
A typical Check function would look like this:
bool Checker::Check1()
{ double result;
// lots of code
m_results.SetCheck1Result(result);
}
And the results class looks something like this:
class Results
{ double m_check1Result;
double m_check2Result;
// ...
public:
void SetCheck1Result(double d);
double GetOverallResult()
{ return max(m_check1Result, m_check2Result, ...); }
};
Note: all code is oversimplified.
The Checker and Result classes were initially written to perform all checks and return an overall double result. There is now a new requirement where I only need to know if any of the results exceeds 1. If it does, subsequent checks need not be carried out(it's an optimisation). To achieve this, I could either:
Modify every CheckN function to keep check for result and return. The parent Check function would keep checking m_results. OR
In the Results::SetCheckNResults(), throw an exception if the value exceeds 1 and catch it at the end of Checker::Check().
The first is tedious, error prone and sub-optimal because every CheckN function further branches out into sub-checks etc.
The second is non-intrusive and quick. One disadvantage is I can think of is that the Checker code may not necessarily be exception-safe(although there is no other exception being thrown anywhere else). Is there anything else that's obvious that I'm overlooking? What about the cost of throwing exceptions and stack unwinding?
Is there a better 3rd option?
I don't think this is a good idea. Exceptions should be limited to, well, exceptional situations. Yours is a question of normal control flow.
It seems you could very well move all the redundant code dealing with the result out of the checks and into the calling function. The resulting code would be cleaner and probably much easier to understand than non-exceptional exceptions.
Change your CheckX() functions to return the double they produce and leave dealing with the result to the caller. The caller can more easily do this in a way that doesn't involve redundancy.
If you want to be really fancy, put those functions into an array of function pointers and iterate over that. Then the code for dealing with the results would all be in a loop. Something like:
bool Checker::Check()
{
for( std::size_t id=0; idx<sizeof(check_tbl)/sizeof(check_tbl[0]); ++idx ) {
double result = check_tbl[idx]();
if( result > 1 )
return false; // or whichever way your logic is (an enum might be better)
}
return true;
}
Edit: I had overlooked that you need to call any of N SetCheckResultX() functions, too, which would be impossible to incorporate into my sample code. So either you can shoehorn this into an array, too, (change them to SetCheckResult(std::size_t idx, double result)) or you would have to have two function pointers in each table entry:
struct check_tbl_entry {
check_fnc_t checker;
set_result_fnc_t setter;
};
check_tbl_entry check_tbl[] = { { &Checker::Check1, &Checker::SetCheck1Result }
, { &Checker::Check2, &Checker::SetCheck2Result }
// ...
};
bool Checker::Check()
{
for( std::size_t id=0; idx<sizeof(check_tbl)/sizeof(check_tbl[0]); ++idx ) {
double result = check_tbl[idx].checker();
check_tbl[idx].setter(result);
if( result > 1 )
return false; // or whichever way your logic is (an enum might be better)
}
return true;
}
(And, no, I'm not going to attempt to write down the correct syntax for a member function pointer's type. I've always had to look this up and still never ot this right the first time... But I know it's doable.)
Exceptions are meant for cases that shouldn't happen during normal operation. They're hardly non-intrusive; their very nature involves unwinding the call stack, calling destructors all over the place, yanking the control to a whole other section of code, etc. That stuff can be expensive, depending on how much of it you end up doing.
Even if it were free, though, using exceptions as a normal flow control mechanism is a bad idea for one other, very big reason: exceptions aren't meant to be used that way, so people don't use them that way, so they'll be looking at your code and scratching their heads trying to figure out why you're throwing what looks to them like an error. Head-scratching usually means you're doing something more "clever" than you should be.