Parse error at 'class' 'properties' 'methods' and 'end', "usage might be invalid syntax"

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Gabriel McQueen 2021-7-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/881313-parse-error-at-class-properties-methods-and-end-usage-might-be-invalid-syntax

评论： Steven Lord 2021-7-19

Unsure where I went wrong, any help would be greatly appreciated.

code:

classdef sData
    %declaration of sample data
    properties
        sId;
        sLength;
        sRadius;
        sDensity;
        sGold;
        sSulfur;
        sArsenic;  
    end
    properties (Dependent)
        goldW;
        sulfurW;
        arsenicW;
    end
    methods
        %objection definition titled sample
        function sample = sData(id, l, r, d, g, s, a, gW, sW, aW)
            sample.sId = id;
            sample.sLength = l;
            sample.sRadius = r;
            sample.sDensity = d;
            sample.sGold = g;
            sample.sSulfur = s;
            sample.sArsenic = a;
            sample.goldW = gW;
            sample.sulfurW = sW;
            sample.arsenicW = aW;
            
        end
        %sample total weight function
        function [sampleWeight] = weight(sample)
            volume = sample.sLength*sample.sRadius^2*pi;
            sampleWeight = volume*sample.sDensity;
        end
        %gold, sulfur, and arsenic weight calculation
        function [gW, sW, aW] = concentrations(sample)
            gW = gold/weight(sample);
            sW = sulfur/weight(sample);
            aW = arsenic/weight(sample);
        end
    end
end

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Walter Roberson 2021-7-19

In class 'sData', no set method is defined for Dependent property 'goldW'. A Dependent property needs a set method to assign its value.

https://www.mathworks.com/help/matlab/matlab_oop/access-methods-for-dependent-properties.html

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Answer 1

Steven Lord 2021-7-19

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https://ww2.mathworks.cn/matlabcentral/answers/881313-parse-error-at-class-properties-methods-and-end-usage-might-be-invalid-syntax#answer_749363

The name of the attribute is Dependent not Dependant.

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Gabriel McQueen 2021-7-19

I corrected the spelling mistake but I get the same errors, do you have advice on this?

Steven Lord 2021-7-19

在 MATLAB Online 中打开

Once I made that correction and tried to create an sData object I did receive an error, though it's a different one than you described.

>> y = sData('abc', 1, 2, 3, 4, 5, 6, 7, 8, 9)
In class 'sData', no set method is defined for Dependent property 'goldW'.  A Dependent property needs a
set method to assign its value.
Error in sData (line 27)
            sample.goldW = gW;

If I had a Circle class with a regular Radius property and a Dependent Area property (that I computed using the Radius whenever the user asked for it), in order to support the user setting a Circle's Area I would need to compute the corresponding Radius and update that property of the Circle.

You need to define property set methods for those three Dependent properties that updates one or more of the properties upon which the Dependent property depends. It would look something like this:

methods
    function obj = set.goldW(obj, newValue)
    end
end

You'll probably also want to define property get methods to be able to retrieve the values of those properties.

The Circle class I described above would have get.Area and set.Area methods, the former of which returns pi*obj.Radius.^2 and the latter of which would set obj.Radius to sqrt(newvalue./pi).

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Parse error at 'class' 'properties' 'methods' and 'end', "usage might be invalid syntax"

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Parse error at 'class' 'properties' 'methods' and 'end', "usage might be invalid syntax"

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