In my program when two functions with the same name are defined for the same table, I want my program to give an error. What's happening is that it's simply just calling the last function and executing it.
Here's a sample code
Class{'Cat'}
function Cat:meow( )
print("Meow!")
end
function Cat:meow()
print("Mmm")
end
kitty = Cat:create()
kitty:meow()
The result of the execution is only: "Mmm"
Instead I want something like an error message to be given.
Unfortunately, __newindex does not intercept assignments to fields which already exist. So the only way to do this is to keep Cat empty and store all its contents in a proxy table.
I don't know the nature of your OOP library, so you'll have to incorporate this example on your own:
local Cat_mt = {}
-- Hide the proxy table in closures.
do
local proxy = {}
function Cat_mt:__index(key)
return proxy[key]
end
function Cat_mt:__newindex(key, value)
if proxy[key] ~= nil then
error("Don't change that!")
end
proxy[key] = value
end
end
Cat = setmetatable({}, Cat_mt)
Related
We have a script that defines values to names similar to #define in c. For example:
script.m:
ERR_NOERROR = 0;
ERR_FATAL = 1;
This script already exists and is used for value replacement when reading data from files.
Now we have a function (or more) that does some analysis and we would like to use the same definition in this function to avoid magic numbers. But when the script is called from the function we get an error.
Attempt to add "ERR_NOERROR" to a static workspace.
See MATLAB Programming, Restrictions on Assigning to Variables for details.
And this does not help much in the understanding of the problem.
The question is how can we make these definitions visible/usable in the functions with having to copying it every time.
Example:
function foo = bar(a)
run(script.m) %also tried running it without the run command
if a == ERR_NOERROR
foo = 5;
else
foo = 6;
end
end
edit:
There was a nested function,below in the function which I was not aware of. This explains the problem.
This kind of scoping error happens when you use nested or anonymous function within a function. The solution is well documented.
To your case, you can avoid nested function, or "Convert the script to a function and pass the variable using arguments", as the documentation suggests.
EDIT: I should have made it clear that the error occurs even if the script is not called within the nested function. Similar scenario is that, in debug mode (by setting up a break point), it will be an error if one tries to create a temporal variable to test something.
This is not a direct answer, rather a recommendation to switch to another method, which will not be mixing scope and workspace.
Instead of defining your constant in a script, you could make a class containing only constant properties. ex: code for error_codes.m:
classdef error_codes
% ---------------------------------------------------------------------
% Constant error code definition
% ---------------------------------------------------------------------
properties (Constant = true)
noerror = 0 ;
fatal = 1 ;
errorlvl2 = 2 ;
errorlvl3 = 3 ;
warning = -1 ;
% etc ...
end
end
I use this style for many different type of constants. For tidiness, I groups them all in a Matlab package directory (The directories which starts with a + character.
The added benefit of using constant class properties is the safety that the values cannot be changed in the middle of the code (your variables defined in a script could easily be overwritten by a careless user).
So assuming my file error_codes.m is placed in a folder:
\...somepath...\+Constants\error_codes.m
and of course the folder +Constants is on the MATLAB path, then to use it as in your example, instead of calling the script, just initialise an instance of the class, then use the constant values when you need them:
function foo = bar(a)
ERR = Constants.error_codes ;
if a == ERR.noerror
foo = 5;
else
foo = 6;
end
or it can works in switch statement too:
switch a
case ERR.noerror
foo = 5 ;
case ERR.warning
foo = 42 ;
case ERR.fatal
foo = [] ;
end
I know that, inside a MATLAB function, inputname(k) will return the k-th argument iff the argument is a variable name. Is there any way to write some parsing code that can retrieve the full input argument when that argument is a structure, e.g. foo.bar ? The reason I want to be able to do this is that I'm writing some tools for generic use where the input could be either a named variable or a named structure element.
My primary intent is to be able to store and return the input argment(s) as part of a structure or other variable that the function returns. This is a 'chain of custody' feature which makes it easier for me or others to verify the source data sets used to generate the output data sets.
I don't want the user to have to self-parse externally, or to have to deal with some kludge like
function doit(name,fieldname)
if(exist('fieldname','var'))
name = name.(fieldname);
myinput = [inputname(1),inputname(2)];
else
myinput = inputname(1);
end
% do the function stuff
(I call this a kludge because it both requires the user to enter strange arguments and because it fouls up the argument sequence for functions with multiple inputs)
There is no support from the language to get the input names when passing structs. The reason is probably x.a is internally a call to subsref which returns a new variable, all context is lost. The only possibility you have is using the debug tools and parse the code. There is no other option.
function x=f(varargin)
[ST, I] = dbstack('-completenames', 1);
if numel(ST)>0
fid=fopen(ST(1).file,'r');
for ix=2:ST(1).line;fgetl(fid);end
codeline=fgetl(fid);
fclose(fid);
fprintf('function was called with line %s\n',codeline);
else
fprintf('function was called from base workspace\n');
end
end
From there you may try to parse the code line to get the individual argument names.
Far uglier than Daniel's approach, and probably will crash on the wrong OS, but here's a hack that works to retrieve the first argument; easily adjusted to retrieve all arguments.
[~,myname] = system('whoami');
myname = strtrim(myname(4:end)); % removes domain tag in my Windows envir
% sorry about " \' " fouling up SO's color parsing
myloc = ['C:\Users\' , myname , '\AppData\Roaming\MathWorks\MATLAB\R2015a\History.xml'] ;
f = fopen(myloc,'r');
foo = fscanf(f,'%s');
fclose(f);
pfoo = findpat(foo,'myFunctionName');
% just look for the last instance
namstart = find(foo(pfoo(end):(pfoo(end)+30)) =='(',1) +pfoo(end);
% catch either ')' or ','
namend(1) = find(foo((namstart):end)== ')',1) -2 +namstart;
if numel(find(foo((namstart):end)== ',',1)),
namend(2) = find(foo((namstart):end)== ',',1) -2 +namstart;
end
thearg = foo(namstart:(min(namend)) );
I need to make several detours to various functions and doing it one by one is just not an option. I'm looking for a function that will take a table, ideally, and this table is class. Loop through it and for each key, value pair that is a function make a function pointer with a prefix before the original function name. I have tried several variations to achieve this effect, but they all yield different problems. Some simply will not make detour pointer no matter what you give to them, others make detour pointers but they don't work, and some will overflow the stack or simply not be recognized.
I want to know if there is a way, ie rawsets, metatable overrides, constant looping until they do match, etc to make it so the function can get a table (or a string that has the same name as the table, thus a loadstring method would work here too) and loop through each function and make a working detour pointer...no matter what.
I prefer using the self:prefix_orig_name(...) syntax [... can be replaced with actual args].
Here's 2 variations I have tried with example useage.
-- 1st Method
detours = detours or {}
function detour(object, class) -- Class is an extra arg that I would send if for some reason just sending an object didn't work...it was theory oh'ed
if detours[object] then -- Check if the detour already exists...might be worth remaking it especially if the function gets overridden several times in different places?
print("detour: Previous " .. object .. " detour found, using previous detour")
return
end
for name, func in pairs(class and class or loadstring("return " .. object)()) do
-- the loadstring method here is used because the argument received is a string of the same name as the table...thus loading it will yield a table
if type(func) == "function" then
local execute, error = loadstring(object .. ".custom_detour_" .. name .. " = " .. object .. "." .. name) -- This makes the actual pointer
if error then
print("detour Error: " .. " Failed to detour: " .. object .. " Error: " .. error)
end
local luanch, assert = pcall(execute)
if not luanch then
print("detour Error: " .. " Failed to detour: " .. object .. " Error: " .. assert)
end
end
end
print("Table: " .. object .. " successfully detourd")
detours[object] = true -- tells us we made a detour of this table/string
end
-- 2nd Method
function detour(object) -- Takes a table
for k, v in pairs(object) do
if type(v) == "function" and not detours[k] then
if not object.custom_detour_ then
object.custom_detour_ = clone(object) -- use a simple cloning function (shallow) to put a clone of the main table into a sub table of the main table
end
if object["custom_detour_" .. k] ~= object.custom_detour_[k] then
object["custom_detour_" .. k] = object.custom_detour_[k] -- this makes it so the self:custom_detour_orig_name(...) syntax can be used, if I am not mistaken
end
end
end
end
-- Example Usage:
MyClass = class() -- class function is relatively OOP standard
function MyClass:init()
self._something = true
end
function MyClass:change(value)
self._something = value
end
function MyClass:table_print(tbl) -- just making funcs up
for k, v in pairs(tbl) do
print(v)
end
end
my_class = MyClass:new()
-- 1st Method
detour("MyClass")
--2nd Method
detour(MyClass)
I personally prefer the 1st method or at least a string, because I can log each detour and if a problem arises later on, it makes debugging easier...but I am for whatever will work.
Simple detouring is easy to do with closures; no need for loadstring:
function detour(cls)
local detours = {}
for key, value in pairs(cls) do
if type(value) == "function" then -- note: ignores objects with __call metamethod
detours["custom_detour_"..key] = function(...)
-- Do whatever you want here
return value(...)
end
end
end
for key, value in pairs(detours) do
cls[key] = value
end
end
This code in lua will apply a function to a value
function Apply(f, value)
return f(value)
end
I can then use it like this apply arbitrary functions calls on my game object like so
Apply(Draw, GameObject)
Apply(Update, GameObject)
Is it possible to instead do what I would, probably incorrectly, call a higher order method
function GameObject:Apply(f)
return self:f()
end
What I eventually want to do is have a table of GameObjects, that I can call Methods on in batch. So using this "higher order method" concept that may not even exist I would create code that does the following.
...
--Create the batch object with three bullets in it
BatchGameObjects = BatchGameObject:new(Bullet1, Bullet2, Bullet3)
--Call equivelent to
--Bullet1:DrawMethod()
--Bullet2:DrawMethod()
--Bullet3:DrawMethod()
--Bullet1:UpdateMethod()
--Bullet2:UpdateMethod()
--Bullet3:UpdateMethod()
BatchGameObjects:Apply(DrawMethod)
BatchGameObjects:Apply(UpdateMethod)
You'll probably want to pass function NAME if you're dealing with methods on other objects, because methods with same name on different objects may resolve to very different functions.
function BatchGameObjects:Apply(function_name)
-- ... or iterate on objects in any other way that matches how you store them ...
for idx = 1, #self.object_list do
local object = self.object_list[idx]
object[function_name](object)
end
end
function GameObject:Apply(f)
return f(self)
end
I am trying to implement save/load functions in a MATLAB (R2009a) UI. My object implements a layout function that generates a user interface for the object. I am trying to implement the callbacks for the save/load buttons. The save button works and save the object out to a MAT file which can be loaded later.
My problem is implementing the callback for the load button. I cannot seem to get the load to load the data from the MAT file and update the properties of the new object. Any suggestions on where I am going wrong along with suggestions on how I might proceed is greatly appreciated.
The important code is my class definition file of course my actual object implements many more properties and methods but here is a skeleton of what I have
classdef myObj<handle
properties
image % property holds a matlab image matrix
objCount % number of objects in image
end
properties(Transient=true)
parent
children
end
methods
function myObj
% empty constructor
end
function load_object(self)
% ask user for file
[fileName, pathToFile]=uigetfile('*.mat','Select .mat file');
tmp = load(fullfile(pathToFile,fileName);
if isfield(tmp,'obj')
self = tmp.obj;
end
end
LayoutFcn(self) % UI layout function
end
end
The UI layout is defined in a seperate file LayoutFcn.m which basically looks like
function LayoutFcn(self)
% create figure window and add various UI elements
...
% create load button
self.children(end+1) = uipushtool('Parent',hToolbar, ... % set parent to current toolbar
'CData',iconRead('open-document.png'), ... % read icon image from file
'Tag','uiLoad', ...
'ClickedCallback',#(hObj,event)loadingMyObject(self,hObj,event));
% create save button
self.children(end+1) = uipushtool('Parent',hToolbar, ... % set parent to current toolbar
'CData',iconRead('save-document.png'), ... % read icon image from file
'Tag','uiSave', ...
'ClickedCallback',#(hObj,event)savingMyObject(self,hObj,event));
...
end
function loadingMyObject(self,hObj,event)
self.load_object; % call load_object method defined above in class definition
end
function savingMyObject(self,hObj,event)
[fileName,pathName]=uiputfile('.mat','Save object to MAT file');
obj = self;
save(fullfile(pahtName,fileName),'obj')
end
Note: I am using MATLAB R2009a.
The code doesn't throw any errors. The way I wrote the code the parent object (represented by self) does not get updated after the call to LOAD in the method load_object. SO, this has the desired effect:
>> var = myObj;
>> var.load_object;
However, if I use the loadingMyObject callback defined in LayoutFcn.m in this fashion
>> var = myObjl
>> var.LayoutFcn
-> click Load button to call _loadingMyObject_
doesn't affect var properties. That is var will still have its default property values after clicking the Load button.
Changing the load methods to use set as suggested by gnovice throws the following error
??? Error using ==> set
Conversion to double from FujiCalibration is not possible.
even though I have set/get methods for each property; as in
method set.image(self,II)
% ... some data validation code ...
self.image = II
end
Using a loop to set each field as suggested by Mr Fooz is not really an option as my full class has public constant that throw an error when they are set.
I am looking for a solution that would avoid me having to hand code setting each field individually. Although at this point it seems like the only possibility.
I believe Mr Fooz is right. The self variable passed to load_object is an object of type "myObj", but the line:
self = tmp.obj;
is simply overwriting the self variable with the structure stored in tmp.obj. Doing:
self.image = tmp.obj.image;
should instead invoke a set operator for the image property of object self. In the MATLAB documentation there is a sample class definition with a method called "set.OfficeNumber" that illustrates this.
In addition, the following line in your function savingMyObject may be unnecessary:
obj = self;
I think it might make most sense (and make the code a little clearer) if you used the name "obj" in place of the word "self" within your class code (as the documentation tends to do). "self" doesn't appear to be any kind of special keyword in MATLAB (like it may be in other languages). It's just another variable as far as I can tell. =)
EDIT #1:
If the prospect of having to set each property individually in your load_object method doesn't sound like fun, one way around it is if you have a SET method for your object that is designed like the SET method for handle graphics. That SET command can accept a structure input where each field name is a property name and each field value is the new value for that property. Then you would have one call like:
set(self,tmp.obj);
Quite a bit shorter, especially if you have lots of properties to set. Of course, you'd then have to write the new SET method for your object, but the shortened syntax may be worth the extra work if it comes in handy elsewhere too. =)
EDIT #2:
You may be able to use the loop Mr Fooz suggested in conjunction with a try/catch block:
fn = fieldnames(tmp.obj);
for i = 1:numel(fn),
try
self.(fn{i}) = tmp.obj.(fn{i});
catch
% Throw a warning here, or potentially just do nothing.
end
end
Don't assign values to self. All that does is replace the binding to the self variable in the scope of the method call. It does not call a magical copy constructor to replace the object reference in the caller. Instead, copy the fields into self. Try something like:
if isfield(tmp,'obj')
self.image = tmp.obj.image;
self.objCount = tmp.obj.objCount;
end
Combining Mr Fooz's and gnovice's suggestions, I added a SET function with the following definition
function set(self,varargin)
if isa(varargin{1},'FujiCalibration')
tmp = varargin{1};
fns = fieldnames(self);
for i = 1:length(fns)
if strcmpi(fns{i}(1:2),'p_')
self.(fns{i}) = tmp.(fns{i});
end
end
self.calibImage = tmp.calibImage;
else
proplist=fields(self);
for n=1:2:length(varargin)
tmp = proplist(strcmpi(proplist,varargin{n}));
value = varargin{n+1};
switch length(tmp)
case 0
msg = char(strcat('There is no ''', varargin{n}, '''property'));
error('FujiCalibration:setPropertyChk',msg)
case 1
tmp = char(tmp);
self.(tmp) = value;
end
end
end
end
I then modified the load_object method as suggested by gnovice by changing
self = tmp.obj
to
set(self,tmp.obj).
I need to make sure that properties with values I want to persist are prefixed with 'p_'.
Thanks to gnovice and Mr Fooz for their answers.