original (update follows)
I'm working with a lot of anonymous functions, ie functions declared as part of a dictionary, aka "methods". It's getting pretty painful to debug, because I can't tell what function the errors are happening in.
Vim's backtraces look like this:
Error detected while processing function NamedFunction..2111..2105:
line 1:
E730: using List as a String
This trace shows that the error occurred in the third level down the stack, on the first line of anonymous function #2105. IE NamedFunction called anonymous function #2111, which called anonymous function #2105. NamedFunction is one declared through the normal function NamedFunction() ... endfunction syntax; the others were declared using code like function dict.func() ... endfunction.
So obviously I'd like to find out which function has number 2105.
Assuming that it's still in scope, it's possible to find out what Dictionary entry references it by dumping all of the dictionary variables that might contain that reference. This is sort of awkward and it's difficult to be systematic about it, though I guess I could code up a function to search through all of the loaded dictionaries for a reference to that function, watching out for circular references. Although to be really thorough, it would have to search not only script-local and global dictionaries, but buffer-local dictionaries as well; is there a way to access another buffer's local variables?
Anyway I'm wondering if it's possible to dump the source code for the anonymous function instead. This would be a lot easier and probably more reliable.
update
I ended up asking about this a while back on the vim_use mailing list. Bram Moolenar, aka vim's BDFL, responded by saying that "You are not supposed to use the function number." However, a suitable alternative for this functionality has not been suggested, as of early September 2010. It's also not been explicitly mentioned whether or not this functionality will continue to work in subsequent vim releases. I've not tried to do this (or anything else, for that matter) in the recently released vim 7.3.
The :function command tries to stop you from specifying the numbered functions (their name is just a number) but you can trick it using the {...} dynamic function name feature, throw in some :verbose and you have a winner:
:verbose function {43}
function 43()
Last set from /home/peter/test.vim
1 throw "I am an exception"
endfunction
This was not at all obvious in the help docs.
I use the following workaround: I have one plugin that does some stuff like creating commands, global functions for other plugins. It also registers all plugins, so I have a large dictionary with lots of stuff related to plugins. If I see a error I search for a function that produces it using function findnr:
"{{{3 stuf.findf:
function s:F.stuf.findf(nr, pos, d)
if type(a:d)==2 && string(a:d)=~#"'".a:nr."'"
return a:pos
elseif type(a:d)==type({})
for [key, Value] in items(a:d)
let pos=s:F.stuf.findf(a:nr, a:pos."/".key, Value)
unlet Value
if type(pos)==type("")
return pos
endif
endfor
endif
return 0
endfunction
"{{{3 stuf.findr:
function s:F.stuf.findnr(nr)
for [key, value] in items(s:g.reg.registered)+[["load", {"F": s:F}]]
let pos=s:F.stuf.findf(a:nr, "/".key, value.F)
if type(pos)==type("")
return pos
endif
endfor
return 0
endfunction
Here I have this plugin functions in s:F.{key} dictionaries and other plugins' functions under s:g.reg.registered[plugname].F dictionary.
Related
I have a situation where I need to call the following:
function xy(i)
return i,i+8
end
And use its output in another function.
function addition(x,y)
return x+y
end
Is there a way to get this to work more elegantly than writing it like:
i.e. i=10; x,y=xy(10); addition(x,y)--28
I'm looking for something like:
i.e. i=10; addition(xy(10)--where I somehow get two arguments here)
Both functions are generics used elsewhere, merging isn't viable, possible edits to what/how they return might be.
At least as of Lua 5.1, the following works 'as requested'.
When a function call is the last (or the only) argument to another call, all results from the first call go as arguments. [There are several examples using print.]
function xy(i)
return i,i+8
end
function addition(x,y)
return x+y
end
addition(xy(10)) -- 28
A more wordy way, that might be useful to decompose in similar cases needing a little bit more flexibility, is to convert the result to a table and then use unpack (added in 5.1). This approach is result -> table -> unpack -> arguments (per above).
addition(unpack({xy(10)})) -- 28
Here are both approaches in replit.
For code append(slice1, 1), Go compile will give error "append(...) evaluated but not used". And we have to use like slice1 = append(slice1,1) because append doesn't modify slice1 and it will return a new slice.
I think it is a good hint since this will prevent lots of bug since we often didn't know function like append will change original array or not. In JavaScript array1.push('item') will change array1 in place and return new length of the array.
I want to utilize this kind of code checking:
func appendStr(str string, tail string) string {
b := str + tail
return b
}
a := "a"
appendStr(a, "b")
But Go compiler didn't give error. So compiler do some special checking on append method? Since Go pass parameter by value, Compiler should know appendStr has no change to modify pass-in parameter.
append() is special because it's a built-in function, and the compiler does extra check on it. It is very rarely useful to not use the return value of append(), so the Go authors decided to make it a compile-time error if it is not used.
On the other hand, calling "ordinary" functions which have return values often have "side effects", and it's common to just call a function for its "side effects" and not use its return values. A very common example is fmt.Println(): you often print something to the console, and you rarely (if ever) check if that succeeds or how many bytes were actually written.
The language spec allows you to not use the return values of functions, so it's valid to do so and you can't force the compiler to make an error or warning out of it, you can't make the compiler to "mark" valid code with error.
See related question: Return map like 'ok' in Golang on normal functions
The way this is typically done in Go is by using an extra tool, a linter if you will. go vet is commonly used to point out things in the code that "don't look right" and which are probably bugs. It seems that you cannot make it check your own functions out-of-the-box, only things like fmt.Sprintf will be checked.
Another tool is errcheck which reports ignored errors.
You could fork one of these tools and insert your own function(s) there, then make everyone check their code before committing it to source control or check it automatically.
I am using QTP 11.5 for automating a web application.I am trying to call an action in qtp through driverscript as below:
RFSTestPath = "D:\vf74\D Drive\RFS Automation\"
LoadAndRunAction RFStestPath & LogInApplication,"Action1",oneIteration
Inside the LogInApplication(Action1) am calling a login function as:
Call fncLogInApplication(strURL,strUsesrName,strPasssword)
Definition of fncLogInApplication is written in fncLogInApplication.vbs
When I associate the fncLogInApplication.vbs file to driverscript, am able to execute my code without any errors. But when I de-associate .vbs file from driverscript and associate it to LogInApplication test am getting "Type mismatch: 'fncLogInApplication'"
Can anyone help me in the association please. I want fncLogInApplication to be executed when I associate to LogInApplication not to the main driverscript.
Please comment back if you require any more info
There is only one set of associated libraries that is active at any one time: That is always the outermost test's one.
This means if test A calls test B, test B will be executed with the libraries loaded based upon test A´s associated libraries list, not B's.
This also means that if B depends on a library, and B associated this library, but is called from test A (which does not associated this library), then B will fail to call (locate) the function since the associated libraries of B are never loaded (only those from A are). (As would A, naturally.).
If you are still interested: "Type mismatch" is QTPs (or VBScript´s) poor way of telling you: "The function called is not known, so I bet you instead meant an array variable dereference, and the variable you specified is equal to empty, so it is not an array, and thus cannot be dereferenced as an array variable, which is what I call a 'type mismatch'."
This reasoning is valid, considering the syntax tree of VB/VBScript: Function calls and array variable dereferences cannot be formally differentiated. Syntactically, they are very similar, or identical in most cases. So be prepared to handle "Type mismatch" like the "Unknown function referenced" message that VB/VBScript never display when creating VBScript code.
You can, however, load the library you want in test B´s code (for example, using LoadFunctionLibrary), but this still allows A to call functions from that library once B loaded it and returned from A´s call. This, and all the possible variations of this procedure, however, have side-effects to aspects like debugging, forward references and visibility of global variables, so I would recommend against it.
Additional notes:
There is no good reason to use CALL. Just call the sub or function.
If you call a function and use the result it returns, you must include the arguments in parantheses.
If you call a sub (or a function, and don´t use the result it returns), you must not include the arguments in parantheses. If the sub or function accepts only one argument, it might look like you are allowed to put it in parantheses, but this is not true. In this case, the argument is simply treated like a term in parantheses.
The argument "bracketing" aspects just listed can create very nasty bugs, especially if the argument is byRef, also due (but not limited) to the fact that VBScripts unfortunately allows you to pass values for a byRef argument (where a variable parameter is expected), so it is generally a good idea to put paranthesis only where it belongs (i.e. where absolutely needed).
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.