MATLAB：使用inputParser和varargin

Question

I have a function for which I would like to pass in arguments via varargin , and use the inputParser to ensure the inputs are sane. Some arguments are required, and some are not. Here is an example:

function myFunc(varargin)
    p = inputParser;
    p.addRequired(...
            'numStates', ...
                @(x) validateattributes(x, {'numeric'}, ...
                {'scalar', 'integer', 'positive'}));
        p.addRequired(...
            'numInps', ...
                @(x) validateattributes(x, {'numeric'}, ...
                {'scalar', 'integer', 'positive'}));
        p.addRequired(...
            'numOuts', ...
                @(x) validateattributes(x, {'numeric'}, ...
                {'scalar', 'integer', 'positive'}));
        p.addRequired(...
            'X0', ...
                @(x) validateattributes(x, {'numeric'}, ...
                {'vector'}));
        p.addOptional(...
            'freq', 10, ...
                @(x) validateattributes(x, {'numeric'}, ...
                {'scalar', 'integer', 'positive'}));
        p.addOptional(...
            'SimulinkVariables', struct(), ...
                @(x) isa(x, 'struct'));

    p.parse(varargin{:});

    %# do stuff with variables
end

I would like to be able to pass in arguments as follows; it should not matter which pair gets passed in when, as long as the required ones are there. So a sample call might be:

myFunc('numStates', 4, 'numInps', 2, 'numOUts', 3, 'X0', [4;0]);

Apparently, this syntax is illegal; parse() expects that the first arguments in it are the required values, but they should not be explicitly named, ie, as in:

function myFunc(numStates, numInps, numOuts, X0, varargin)
    ...
    p.parse(numStates, numInps, numOuts, X0, varargin{:});

end

Is there a simple way to make this do what I want, ie, the first function? I guess the easiest thing to do is do something to reorder the elements of varargin and kick out the argument names, but that isn't terribly elegant.

Answer 1

The most elegant solution I can think of is to subclass inputParser . So you could do something like this (save as myInputParser.m):

classdef myInputParser < inputParser
    properties
        required = {};
    end

    methods
        function obj = myInputParser
            obj = obj@inputParser;
        end

        function addRequired(obj, argname, validator)
            obj.required = {obj.required{:}, argname};
            obj.addOptional(argname, [], validator);
        end

        function parse(obj, varargin)
            params_input = varargin(1:2:end);
            for i=1:length(obj.required)
                if isempty(strmatch(obj.required{i}, params_input))
                    error(sprintf('Required named parameter %s was not passed to function', obj.required{i}));
                end
            end
            parse@inputParser(obj, varargin{:});
        end

    end
end

Then change

    p = inputParser;

to

    p = myInputParser;

and then your code will work as you want it to.

Note that this might not handle all edge cases correctly, and I haven't tested it extensively, but it does work with your example use case.

Answer 2

In InputParser you can add ParameterName - ParameterValue pairs only with addParamValue . Those arguments are supposed to be optional.

As a workaround you can add all your parameters with addParamValue and use [] as default value for required arguments.

Then you can do one of the following:

• add 'nonempty' to attributes in validateattributes function for required arguments ( however in this case the error message will not say this is required arguments, but that it has to be non-empty )
• or add separate check (with if or assert ) that required arguments should be not-empty with your own error message.

You are not limited to use [] . The default can be any value not appropriate for a particular parameter and easy to check.