Alternative to using EVAL
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Hi All,
I need to call a function whose name is decided dynamically at runtime. Is there an alternative to using the eval function?
My requirement is this: I have a Matlab application with a non-linear optimisation model as the core solver for this application. I need the user to have the option to "plug and play" different models without needing to rewrite the code.
Currently I have solved this requirement by having a string array containing the name of the model function (e.g. LoadModelPkg = 'myModel'). The user can change this using a dialog box.
My application then calls this function using the following lines of code:
LoadModelPkg = 'myModel' % name of the function to call.
LoadModelPkgCall = ['[jfit, estParams, graphData] = ', LoadModelPkg, '(tr, Pr, Qr, Avr, powerfactor, WarmStartIdx, graphDataStruct);']; % create the function call
eval(LoadModelPkgCall)
This works, but the Matlab debugger warns that the variables in the above LoadModelPkgCall string are unused. Is there an alternative to using the eval function?
Thanks for the help.
Andrew
采纳的回答
If the name of your function must really be a string, you'll want to use STR2FUNC to build a function handle out of the string, and then use it as in Azzi's answer.
fn = 'MyModel' ; % Function name, coming from elsewhere.. e.g. some user
% input management mechanism.
fh = str2func(fn) ; % Function handle.
[jfit, estParams, graphData] = fh(tr, Pr, etc..) ;
4 个评论
Andrew
2013-3-4
Walter Roberson
2013-3-4
str2func works well. There are some subtle differences one could get into if the user is allowed to change the package code while using the program (do the conversion once and pass around the handle if you want to capture the function as of a particular time; do the conversion at each location if you want the newest version to be used.)
I meant that if you give the user to possibility to choose between pred-defined models/functions that you (and only you) define, then handles to these functions are the way to go (no need to use STR2FUNC). Also when you want to give users the possibility to "pass a function" to your function, handles are the way to go (i.e. I, as a user, prefer to pass a handle to a function that I chose than the name of this function as a string). Now if there is a GUI involved and users can define some path + function name, it is better/simpler to accept a function name as a string and convert it into a handle using STR2FUNC, than to use some complicated construct based on EVAL. So I think that there is no better alternative than what you ended up implementing!
Andrew
2013-3-5
更多回答（1 个）
Azzi Abdelmalek
2013-3-3
If your goal is to use different functions
f=@myModel
[jfit, estParams, graphData] = f(tr, Pr, Qr, Avr, powerfactor, WarmStartIdx, graphDataStruct);
1 个评论
Azzi Abdelmalek
2013-3-4
编辑：Azzi Abdelmalek
2013-3-4
You can create a function where you will past a handle function, You will need also to use str2func as suggested by Cedric.
Example
function y=fcn(f,data,choice)
% y and data are cell array
% f is you function
if choice==1
[a,b]=f(data{1},data{2})
y={a,b}
elseif choice==2
y=f(data{1}
else
[a,b,c}=f(data{1},data{2},data{3})
y={a,b,c}
end
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