Argument validation and config file

Question

Martin Hock 2022-3-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1677494-argument-validation-and-config-file

回答： Ravi 2023-12-21

We've written a little tool andsome options can be stored in a config file.

So for options, they can be read from the config file or handed over manually as name/value-pairs, and we also have defaults defined in the argument validation.

At this point, the config file takes priority over default and manual input, because it is read after the argument validation, and we cannot differentiate between manual inputs and defaults after the validation.

I'll add some code to show what the issue is.

function math(numbers, options)
    arguments
        numbers (1,1) {mustBeNumeric} = [1,1]
        options.basic (1,:) {mustBeText} = 'add'
    end
 % At this point I don't know, whether options.basic is from argument or default   
 
 % test for config file
 if exist('config.json')
     configfromfile = jsondecode('config.json');
     if isfield(configfromfile,basic)
         options.basic = configfromfile.basic;
     end % Overwriting with config file.
     
 end
% do maths here
switch basic
    case 'add'
        add(numbers)
end
end

So at the moment the priority is config file > argument > default

But obviously we'd want to have a "user defined default" in the config file, and possible adjustments via argument: argument > config file > default.

The only way I can think of doing this is by using a wrapper, that is already testing the config file and reading its values, and compiling options for the inner function.

function math(numbers, options)
    
% test for config file
if exist('config.json')
    configfromfile = jsondecode('config.json');
    for i=fieldnames(configfromfile)
       if ~isfield(options.(i)) % manual input gets priority
           options.(i)=configfromfile.(i)
       end
    end
end
realmath(numbers, options)
end
  
function realmath(numbers, options)
arguments
        numbers (1,1) {mustBeNumeric} = [1,1]
        options.basic (1,:) {mustBeText} = 'add'
end
% do maths here
switch basic
    case 'add'
        add(numbers)
end
end

So what would be the elegant way to handle this?

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Answer 1

Ravi 2023-12-21

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Hi Martin Hock,

Please find an approach for prioritizing the inputs in the order arguments > config > default.

function math(numbers, options) 
    % Define the default options 
    defaultOptions = struct('basic', 'add'); 
    
    % If a config file exists, read it and merge with default options 
    if exist('config.json') 
        configOptions = jsondecode(configFile); 
        optionsFromConfig = mergeOptions(defaultOptions, configOptions); 
    else 
        optionsFromConfig = defaultOptions; 
    end 
    
    % If options are provided manually, merge them with options from config 
    finalOptions = mergeOptions(optionsFromConfig, options); 
    
    % Do the math operation based on the final options 
    switch finalOptions.basic 
        case 'add' 
            % Call the add function with the provided numbers 
            result = add(numbers); 
    end 
end 
function mergedOptions = mergeOptions(defaults, overrides) 
    % Merge two structures, where fields in 'overrides' take precedence 
    mergedOptions = defaults; 
    overrideFields = fieldnames(overrides); 
    for i = 1:numel(overrideFields) 
        mergedOptions.(overrideFields{i}) = overrides.(overrideFields{i}); 
    end 
end 

We create a variable “defaultOptions” to store the defaults. We check for the “config.json” file and if it exists we merge the options with the already created “defaultOptions”. In this situation, the “config.json” gets priority over “defaultOptions” and if any variable present in “config.json” is already present in “defaultOptions”, then it gets overridden.

Next, we create a variable, “finalOptions” that combines the options from config file, default options, and passed arguments.

The “mergeOptions” function takes two arguments; second one takes higher priority over the other. The variables are overridden with the second argument.

Hope this helps.

Thanks,

Ravi Chandra