Hello,
Or when you have to write a function following a specific prototype (
graphic events, optim, ode, ...)
If I would write a function that call another, I have to specify a
prototype to allow user to call my function.
But in some case, the final user does not need all parameters so he can
replace unused inputs by ~.
I think that only syntactic sugar.
example:
function for_each(iterable, fn)
for i=1:size(iterable, "*")
fn(iterable(i), i, iterable); //item, index, array
end
endfunction
Users can define fn like this if tthey only need item and don't want to
use index and whole array
function my_func(a, ~, ~)
//blabla
end
I don't say that's essential :p
That's my understanding
Antoine
Le 26/11/2019 à 16:15, Chin Luh Tan a écrit :
Hi Samuel,
In fact I've not been using matlab for more than 10 years, so I try to
understand this as well.
The input tilde is still abit confusing for me as well, I am trying to
understand its' usage as this page:
https://octave.org/doc/v4.4.1/Ignoring-Arguments.html
function val = pick2nd (~, arg2)
val = arg2;
endfunction
I can't see the reason why the input need to ignored in this case, is
it defined but not being user due to bad user overlooked it? or is it
neglected and the default value would be used?
Then I find this :
https://stackoverflow.com/questions/25204074/correct-use-of-tilde-operator-for-input-arguments
*/"The tilde is only for function declaration. Matlab's mlint
recommends to replace unused arguments by ~. The result is a function
declared like this function output = MyFunction(a, b, ~, c). This is a
very bad practice. /**/
/*
*/
/*
*/Since you have a function where the parameters are optional, you
must call the function with empty arguments
output=MyFunction(str1,str2,[],[],...,true)."/*
It sound to me that the input tilde is suggested by the matlab mlint
to improve the code so that the unused variable need not to pass into
the function, and to improve memory management?
So there are 2 possibilities for the input tilde :
1. used to replace unused variable in the input which defined by user,
but not being used. So the mlint recomment to replace with tilde, it
could be be remove possibly due to the project has been calling the
functions for many time, and changing the 4th to 3rd argument might
need to change a lot of codes. In this case, the %unused would be good.
2. Tilde used to tell the function to use default value, then
replacing it with % unused might cause error.
Think we need some x-matlaber to confirm which case.
Thanks again.
rgds,
CL
---- On Tue, 26 Nov 2019 20:36:01 +0800 *Samuel Gougeon
<sgoug...@free.fr <mailto:sgoug...@free.fr>>* wrote ----
Hello Chin Luh,
Thanks a lot for your input.
Both cases -- input and output will have to be converted --, since
the converter is also made to convert (sets of) functions
definitions, not only scripts.
About the input case: Steven's answer is still not really clear to
me. Doing some tests on Octave, we must anyway provide some input
at calling time when ~ is used as default input in the
definition. AFAIU, this ~ could just be to make sure that no
variable name used inside the function matches the name of the
input argument in the function definition, since "~" alone can't
be actually used as variable's name. In this case, for Scilab, any
input ~ could be replaced with an improbable variable name like
"%unused" or "%kwzxq", and that should do it.
Please, correct me if someone understands something else.
Best regards
Samuel
Le 26/11/2019 à 03:33, Chin Luh Tan a écrit :
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Hi Samuel,
I think your assumption likely correct on the input and the
output using ~
https://www.mathworks.com/matlabcentral/answers/288016-tilde-doesn-t-work-for-ignoring-my-inputs
"
You *can*use tilde to ignore input arguments when you
*define*the function.
You *cannot*use tilde to ignore input arguments when you
*call*the function.
You *cannot*use tilde to ignore output arguments when you
*define*the function.
You *can*use tilde to ignore output arguments when you
*call*the function.
If you want to be able to specify only the third argument,
there must be some way for your function to disambiguate the
one-input call from a call that specifies only the third
input. Usually in MathWorks function this is done by
specifying [] for the arguments for which the user doesn't
want to specify. In that case the code would use the default
value if either narginis too small or if narginis large enough
and the specified input argument isempty.
"
From what I could think off, mat2sci conversion to replace ~
at the output arguments should always be safe. As for the
input, since the tilde could not be used as input when calling
function, I think there should not be any cases that need to
be implemented in conversion?
Thanks.
Regards,
CL
---- On Tue, 26 Nov 2019 04:20:52 +0800 *Samuel Gougeon
<sgoug...@free.fr> <mailto:sgoug...@free.fr>* wrote ----
Le 23/11/2019 à 15:35, Samuel Gougeon a écrit :
HelloPhilipp, and to all (former ;-) matlabers,
Le 16/10/2019 à 11:46, P M a écrit :
Dear experts,
trying to convert a matlab code to scilab I come
across following line:
[~,~,Minstances_hat] = unique(B(:));
How to replace the "~" symbol?
B is the blue channel of a RGB image...hence a m x
n matrix of integers (type(B) = 8 )
This issue is now reported as bug 16250
<http://bugzilla.scilab.org/show_bug.cgi?id=16254>.
Solving this issue would improve the converter.
I may contribute to solve it. However, I do not use to
use Matlab or Octave. So i don't know how the ~
placeholder set in the list of /inputs/ is processed
inside the called function. This message is a call for
information about this topic.
Ignoring an output is trivial. As suggested by
Stéphane, the ans variable is a good candidate as
replacement for ~,
just as a fake recipient, as in "[~, ia] =
unique(A)" => "[ans, ia] = unique(A)"
The meaning of ignoring an input is a priori
completely different, at least from a Scilab point of
view.
This leads to the fact that, on the "function ..."
line, the converter will have to distinguish the list
of inputs from the list of outputs, and then process
the same ~ character in 2 different ways.
This processing would have to run also when the
"function ..." line is split on several rows with the
"..." continuation marks.
First, i will need an actual example of function call
with ~ in the input list, runnable in Octave.
Any compact suggestion is welcome.
At least 2 use cases are expected: one calling a
function written in Octave/Matlab language (improperly
called "macros" in Scilab), the other one calling a
hard-coded function.
Let's consider the first case, with a "macro":
* What does the ~ sent placeholder pass to the
function? How is it detected/detectable inside the
macro ?
* How is it processed by the function? Is there a
generic default processing, as replacing it with
the empty matrix [], or whatever else?
Where is the crowd of matlabers?
The page describing this
feature:https://fr.mathworks.com/help/matlab/matlab_prog/ignore-function-inputs.html
But i do not clearly understand it.
Apparently, "canceling" an input is done (only?) at the
function definition, not when calling it, unlike for the
outputs.
If so, then /ans/ could also be used as a replacement,
meaning that anyway this input won't be used inside the
function.
A test of call with Octave yields an error:
>> function [r, s] = funtest(a,b,c)
end
>> funtest(1,~,3)
parse error:
invalid use of empty argument (~) in index expression
>>> funtest(1,~,3)
^
>>
Any further insight is welcome.
Samuel
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