At work we often use functions returning a BOOLEAN where the BOOLEAN represents a logical statement and not whether the operation of the function was successfully or not
e.g. BOOLEAN HaseThisValueBeCountedAlready (Value)
When validating the input in this function what would be the best way proceed if invalid input was detected. Some people think to just return FALSE but in my opinion that would just hide the fact that something is wrong and the Caller might proceed doing something with the value not knowing that the answer doesn't make sense.
The function might be globally accessible so it feels a bit weird assuming the caller will validate the input.
Any ideas?
In general, for invalid input that doesn't enable the functions to provide the service/answer, you need to raise an exception.
This way, the guy asking the "question" to the function knows he's not "formulating" it the right way.
if its a value that need to be read periodically , you can assign the output to a global variable ,if it valid or dont update global variable if the input is invalid , so the global variable stays with the previous valid value.
this way , each function need this value , use the global variable with 100% that is valid value.
Related
I was working on a simple task yesterday, just needed to sum the values in a handful of dropdown menus to display in a textbox via Javascript. Unexpectedly, it was just building a string so instead of giving me the value 4 it gave me "1111". I understand what was happening; but I don't understand how.
With a loosely typed language like Javascript or PHP, how does the computer "know" what type to treat something as? If I just type everything as a var, how does it differentiate a string from an int from an object?
What the + operator will do in Javascript is determined at runtime, when both actual arguments (and their types) are known.
If the runtime sees that one of the arguments is a string, it will do string concatenation. Otherwise it will do numeric addition (if necessary coercing the arguments into numbers).
This logic is coded into the implementation of the + operator (or any other function like it). If you looked at it, you would see if typeof(a) === 'string' statements (or something very similar) in there.
If I just type everything as a var
Well, you don't type it at all. The variable has no type, but any actual value that ends up in that variable has a type, and code can inspect that.
so i just came across some code that reads like so:
checkCalculationPeriodFrequency("7D", "7D", SHOULD_MATCH);
and
checkCalculationPeriodFrequency("7D", "8D", SHOULD_NOT_MATCH);
Let's not worry about what the code does for now (or indeed, ever), but instead, let's worry about that last parameter - the SHOULD_MATCH and SHOULD_NOT_MATCH
Its something i've thought of before but thought might be "bad" to do (inasmuch as "bad" holds any real meaning in a postmodernist world).
above, those values are declared (as you might have assumed):
private boolean SHOULD_MATCH = true;
private boolean SHOULD_NOT_MATCH = false;
I can't recall reading about "naming" the boolean parameter passed to a method call to ease readability, but it certainly makes sense (for readability, but then, it also hides what the value is, if only a teeny bit). Is this a style thing that others have found is instagram or like, soooo facebook?
Naming the argument would help with readability, especially when the alternative is usually something like
checkCalculationFrequency("7D",
"8D",
true /* should match */);
which is ugly. Having context-specific constants could be a solution to this.
I would actually go a step further and redefine the function prototype to accept an enum instead:
enum MatchType {
ShouldMatch,
ShouldNotMatch
};
void checkCalculationFrequency(string a, string b, MatchType match);
I would prefer this over a boolean, because it gives you flexibility to extend the function to accept other MatchTypes later.
I suggest you not to do this way.
First, for each object, the two members SHOULD_MATCH and SHOULD_NOT_MATCH are regenerated. And that's not good because it's not a behavior of the object. So it you want to use is, at least describe it as STATIC FINAL.
Second, I prefer to use an enum instead, because you can control completely the value of the param, i.e. when you use it, you must use either SHOULD_MATCH or SHOULD_NOT_MATCH, not just true or false. And this increase the readability too.
Regards.
It is indeed for readability. The idea is that the reader of the function call might not know immediately what the value true mean in the function call, but SHOULD_MATCH conveys the meaning immediately (and if you need to look up the actual value, you can do so with not much effort).
This becomes even more understandable if you have more than one boolean parameters in the function call: which true means what?
The next step in this logic is to create named object values (e.g. via enum) for the parameter values: you cannot pass on the wrong value to the function (e.g. in the example of three boolean parameters, nothing stops me from passing in SHOULD_MATCH for all of them, even though it does not make sense semantically for that function).
It's definitely more than a style thing.
We have a similar system that takes takes input from a switch in the form of boolean values, 1 or 0, which is pretty much the same as true or false.
In this system we declare our variables OPEN = true and CLOSED = false* and pass them into functions which perform different actions depending on the state of the switch. Now if someone happens to hook up the switch differently it may be that we now get the value 0 when it is OPEN and 1 when it is CLOSED.
By having named boolean variables we can easily adapt the system without having to change the logic throughout. The code becomes self documenting because developers can clearer see what action is meant to be taken in which case without worrying what value comes.
Of course the true purpose of the boolean value should be well documented else where and it is in our system....honest....
*(maybe we use OPEN, !OPEN I forget)
I have a VB6 function, which executes an SQL delete. The function returns a boolean depending on whether or not the deletion was successful:
Public Function Delete(ByVal RecordID As Integer) As Boolean
On Error GoTo ErrorGenerated //Execute SQL delete
Delete = True
Exit Function
ErrorGenerated: Delete = False
End Function
I read somewhere that it is better to return an integer, which dictates whether or not the deletion was successful. However, there can only be two outcomes from running the function from what I can see i.e. deleted or not deleted (not deleted if an error is thrown). Is it better to return an integer?
I'd suggest your best bet is to return an enumerated type; each value for the enumeration can then explain to the caller what the problem is in a clear and unambiguous way, and new error reasons can be added later as required without breaking anything. Something like...
Public Enum DB_ERRS
Success
NoConnection
FailedForThisReason
FailedForThatReason
FailedForOtherReason
Failed
End Enum
Then all your database access functions could return a value of this type...
Public Function Delete(ByVal RecordID As Integer) As DB_ERRS
On Error GoTo ErrorGenerated
Execute SQL delete
Delete = Success
Exit Function
ErrorGenerated:
If Err.Number = this Then
Delete = FailedForThisReason
Else
Delete = Failed
End If
End Function
Intellisense will even help you fill them in.
This is rather subjective.
One would say, return a boolean because it's as simple as it gets.
Another one would say, return an integer, because later you might want to add a third status, such as "archived," and it would break existing code.
And someone else would say, Ditch that C-style return codes. Create a sub that doesn't return anything, and raise an exception in case you need to indicate failure.
I personally prefer exceptions. But it's up to you to decide.
In terms of size, an integer is a 32-bit signed integer, while the boolean data type doesn't really have a defined size. However, it also depends on the context from where you've read about using integers over booleans.
For SOME, the difference is irrelevant when using it as a return value from functions.
However, it can be something of a preference in stored procedures if you're also considering the return value from the stored procedure. The evaluation of booleans (when converted to numbers) may lead to it being treated like a bit (0 and 1).. In any case, it's more of a subjective approach. Integers allow more flexibility, while booleans offer limitation and simplicity. Which is better? I think it's almost entirely up to you, your preference, your coding standards, your company's coding standards, or whatnot..
Just to share a link on data types :
http://msdn.microsoft.com/en-us/library/aa383751(v=vs.85).aspx
I'll throw my opinion in. I personally think that returning a boolean value is the right thing to do. Do you really care why it failed to delete? Not normally, there are only a few reasons why a delete could fail in the first place (file locked or lack of permissions). If you need to return the reason for failure so it can be handled differently in some way, then yes, return an integer. Now personally, I don't like magic numbers, so I would never return an integer and would return an enum value instead.
Something like this (yes, this doesn't deal with some edge cases - that's not the point):
int CountDigits(int num) {
int count = 1;
while (num >= 10) {
count++;
num /= 10;
}
return count;
}
What's your opinion about this? That is, using function arguments as local variables.
Both are placed on the stack, and pretty much identical performance wise, I'm wondering about the best-practices aspects of this.
I feel like an idiot when I add an additional and quite redundant line to that function consisting of int numCopy = num, however it does bug me.
What do you think? Should this be avoided?
As a general rule, I wouldn't use a function parameter as a local processing variable, i.e. I treat function parameters as read-only.
In my mind, intuitively understandabie code is paramount for maintainability, and modifying a function parameter to use as a local processing variable tends to run counter to that goal. I have come to expect that a parameter will have the same value in the middle and bottom of a method as it does at the top. Plus, an aptly-named local processing variable may improve understandability.
Still, as #Stewart says, this rule is more or less important depending on the length and complexity of the function. For short simple functions like the one you show, simply using the parameter itself may be easier to understand than introducing a new local variable (very subjective).
Nevertheless, if I were to write something as simple as countDigits(), I'd tend to use a remainingBalance local processing variable in lieu of modifying the num parameter as part of local processing - just seems clearer to me.
Sometimes, I will modify a local parameter at the beginning of a method to normalize the parameter:
void saveName(String name) {
name = (name != null ? name.trim() : "");
...
}
I rationalize that this is okay because:
a. it is easy to see at the top of the method,
b. the parameter maintains its the original conceptual intent, and
c. the parameter is stable for the rest of the method
Then again, half the time, I'm just as apt to use a local variable anyway, just to get a couple of extra finals in there (okay, that's a bad reason, but I like final):
void saveName(final String name) {
final String normalizedName = (name != null ? name.trim() : "");
...
}
If, 99% of the time, the code leaves function parameters unmodified (i.e. mutating parameters are unintuitive or unexpected for this code base) , then, during that other 1% of the time, dropping a quick comment about a mutating parameter at the top of a long/complex function could be a big boon to understandability:
int CountDigits(int num) {
// num is consumed
int count = 1;
while (num >= 10) {
count++;
num /= 10;
}
return count;
}
P.S. :-)
parameters vs arguments
http://en.wikipedia.org/wiki/Parameter_(computer_science)#Parameters_and_arguments
These two terms are sometimes loosely used interchangeably; in particular, "argument" is sometimes used in place of "parameter". Nevertheless, there is a difference. Properly, parameters appear in procedure definitions; arguments appear in procedure calls.
So,
int foo(int bar)
bar is a parameter.
int x = 5
int y = foo(x)
The value of x is the argument for the bar parameter.
It always feels a little funny to me when I do this, but that's not really a good reason to avoid it.
One reason you might potentially want to avoid it is for debugging purposes. Being able to tell the difference between "scratchpad" variables and the input to the function can be very useful when you're halfway through debugging.
I can't say it's something that comes up very often in my experience - and often you can find that it's worth introducing another variable just for the sake of having a different name, but if the code which is otherwise cleanest ends up changing the value of the variable, then so be it.
One situation where this can come up and be entirely reasonable is where you've got some value meaning "use the default" (typically a null reference in a language like Java or C#). In that case I think it's entirely reasonable to modify the value of the parameter to the "real" default value. This is particularly useful in C# 4 where you can have optional parameters, but the default value has to be a constant:
For example:
public static void WriteText(string file, string text, Encoding encoding = null)
{
// Null means "use the default" which we would document to be UTF-8
encoding = encoding ?? Encoding.UTF8;
// Rest of code here
}
About C and C++:
My opinion is that using the parameter as a local variable of the function is fine because it is a local variable already. Why then not use it as such?
I feel silly too when copying the parameter into a new local variable just to have a modifiable variable to work with.
But I think this is pretty much a personal opinion. Do it as you like. If you feel sill copying the parameter just because of this, it indicates your personality doesn't like it and then you shouldn't do it.
If I don't need a copy of the original value, I don't declare a new variable.
IMO I don't think mutating the parameter values is a bad practice in general,
it depends on how you're going to use it in your code.
My team coding standard recommends against this because it can get out of hand. To my mind for a function like the one you show, it doesn't hurt because everyone can see what is going on. The problem is that with time functions get longer, and they get bug fixes in them. As soon as a function is more than one screen full of code, this starts to get confusing which is why our coding standard bans it.
The compiler ought to be able to get rid of the redundant variable quite easily, so it has no efficiency impact. It is probably just between you and your code reviewer whether this is OK or not.
I would generally not change the parameter value within the function. If at some point later in the function you need to refer to the original value, you still have it. in your simple case, there is no problem, but if you add more code later, you may refer to 'num' without realizing it has been changed.
The code needs to be as self sufficient as possible. What I mean by that is you now have a dependency on what is being passed in as part of your algorithm. If another member of your team decides to change this to a pass by reference then you might have big problems.
The best practice is definitely to copy the inbound parameters if you expect them to be immutable.
I typically don't modify function parameters, unless they're pointers, in which case I might alter the value that's pointed to.
I think the best-practices of this varies by language. For example, in Perl you can localize any variable or even part of a variable to a local scope, so that changing it in that scope will not have any affect outside of it:
sub my_function
{
my ($arg1, $arg2) = #_; # get the local variables off the stack
local $arg1; # changing $arg1 here will not be visible outside this scope
$arg1++;
local $arg2->{key1}; # only the key1 portion of the hashref referenced by $arg2 is localized
$arg2->{key1}->{key2} = 'foo'; # this change is not visible outside the function
}
Occasionally I have been bitten by forgetting to localize a data structure that was passed by reference to a function, that I changed inside the function. Conversely, I have also returned a data structure as a function result that was shared among multiple systems and the caller then proceeded to change the data by mistake, affecting these other systems in a difficult-to-trace problem usually called action at a distance. The best thing to do here would be to make a clone of the data before returning it*, or make it read-only**.
* In Perl, see the function dclone() in the built-in Storable module.
** In Perl, see lock_hash() or lock_hash_ref() in the built-in Hash::Util module).
This is general programming, but if it makes a difference, I'm using objective-c. Suppose there's a method that returns a value, and also performs some actions, but you don't care about the value it returns, only the stuff that it does. Would you just call the method as if it was void? Or place the result in a variable and then delete it or forget about it? State your opinion, what you would do if you had this situation.
A common example of this is printf, which returns an int... but you rarely see this:
int val = printf("Hello World");
Yeah just call the method as if it was void. You probably do it all the time without noticing it. The assignment operator '=' actually returns a value, but it's very rarely used.
It depends on the environment (the language, the tools, the coding standard, ...).
For example in C, it is perfectly possible to call a function without using its value. With some functions like printf, which returns an int, it is done all the time.
Sometimes not using a value will cause a warning, which is undesirable. Assigning the value to a variable and then not using it will just cause another warning about an unused variable. For this case the solution is to cast the result to void by prefixing the call with (void), e.g.
(void) my_function_returning_a_value_i_want_to_ignore().
There are two separate issues here, actually:
Should you care about returned value?
Should you assign it to a variable you're not going to use?
The answer to #2 is a resounding "NO" - unless, of course, you're working with a language where that would be illegal (early Turbo Pascal comes to mind). There's absolutely no point in defining a variable only to throw it away.
First part is not so easy. Generally, there is a reason value is returned - for idempotent functions the result is function's sole purpose; for non-idempotent it usually represents some sort of return code signifying whether operation was completed normally. There are exceptions, of course - like method chaining.
If this is common in .Net (for example), there's probably an issue with the code breaking CQS.
When I call a function that returns a value that I ignore, it's usually because I'm doing it in a test to verify behavior. Here's an example in C#:
[Fact]
public void StatService_should_call_StatValueRepository_for_GetPercentageValues()
{
var statValueRepository = new Mock<IStatValueRepository>();
new StatService(null, statValueRepository.Object).GetValuesOf<PercentageStatValue>();
statValueRepository.Verify(x => x.GetStatValues());
}
I don't really care about the return type, I just want to verify that a method was called on a fake object.
In C it is very common, but there are places where it is ok to do so and other places where it really isn't. Later versions of GCC have a function attribute so that you can get a warning when a function is used without checking the return value:
The warn_unused_result attribute causes a warning to be emitted if a caller of the function with this attribute does not use its return value. This is useful for functions where not checking the result is either a security problem or always a bug, such as realloc.
int fn () __attribute__ ((warn_unused_result));
int foo ()
{
if (fn () < 0) return -1;
fn ();
return 0;
}
results in warning on line 5.
Last time I used this there was no way of turning off the generated warning, which causes problems when you're compiling 3rd-party code you don't want to modify. Also, there is of course no way to check if the user actually does something sensible with the returned value.