八度：创建一个类变量，然后在类中访问（在构造函数中）

Question

也许这是一个微不足道的问题，但我想知道如何在八度范围内访问类别的恒定属性或类功能。让我们以一个例子：

classdef Example % < FatherClass
    
    % read-only protected properties
    properties (Constant=true, Access=protected)
        all_levels = {"A","B","C","D"};
    endproperties
    
    % protected properties
    properties(Access=protected)
        level = 'D';
        output = '.';
    endproperties

    methods(Access=public)
        function obj = Example (level,outputfilepath)

            if any(strcmp(all_levels,level))
                obj.level = level;
            else
                error ("possible levels are: A B C D");
            endif

            obj.output = outputfilepath

        endfunction

    endmethods
end

运行此类示例我收到错误：

error: 'all_levels' undefined near line 12, column 12
error: called from
    Example at line 12 column 13

所以，我尝试了类似

if any(strcmp(obj.all_levels,level))
     obj.level = level;

结果的尝试，也定义了一个getter：

methods (Static = true)
  function lvs = gel_levels()
     lvs = all_levels
  endfunction
endmethods

...

methods(Access=public)
  function obj = Example (obj,level,outputfilepath)
    all_levels = get_levels()
    % disp(all_levels)
    if any(strcmp(all_levels,level))
       obj.level = level;
    else
       error ("possible levels are: A B C D");
    endif
       obj.output = outputfilepath
  endfunction
endmethods

对不起，但我对Octave是新手，我还没有找到任何有关的例子这。我要完成的是一个简单的类变量

Answer 1

问题有点令人困惑，因为不同的尝试似乎正在使用不同的部分，但是总的来说，您认为您的问题是您不是将对象作为方法中的正式参数传递。

还不清楚您是否试图修改对象“原位”，还是试图生成新的对象...但是无论如何都不可能会记住，不可能修改对象（除非从'hander''继承来目的）。因此，您应该做的典型的事情是：将对象作为第一个输入传递给您应该使用类方法定义，对其进行修改，返回它，然后在调用中使用此方法时工作区，通过分配捕获此对象（通常在变量中以与调用工作区中的所谓对象相同的名称）。

这对我有用：

%% in Example.m
classdef Example

    % read-only protected properties
    properties( Constant=true, Access=protected )
        all_levels = {"A", "B", "C", "D"};
    endproperties

    % protected properties
    properties( Access = protected )
        level  = 'D';
        output = '.';
    endproperties

    methods( Access = public )
        function obj = Logging( obj, level, outputfilepath )
            valid_level_choice = any( strcmp( obj.all_levels, level ) );

            if valid_level_choice,   obj.level = level;
            else,                    error( "possible levels are: A B C D" );
            endif

            obj.output = outputfilepath;
        endfunction

        function get_level( obj )
            fprintf( "The level is %s\n;", obj.level );
        endfunction

    endmethods
endclassdef

%% In your console session
E = Example();
E.get_level()
%> The level is D
E = E.Logging( 'A', './' );
E.get_level()
%> The level is A

更新

更新的代码给定修订的问题/评论。
这在八度的7.1.0中对我有用

%% in Example.m
classdef Example % < FatherClass

    % read-only protected properties
    properties (Constant=true, Access=protected)
        all_levels = {"A","B","C","D"};
    endproperties

    % protected properties
    properties(Access=protected)
        level = 'D';
        output = '.';
    endproperties

    methods(Access=public)
        % Constructor
        function obj = Example (level,outputfilepath)
            valid_choice = any(strcmp(obj.all_levels,level));
            if valid_choice, obj.level = level;
            else, error ("possible levels are: A B C D");
            endif
            obj.output = outputfilepath;
        endfunction
        % Remaining Methods
        function get_level( obj ), fprintf( "The level is %s\n", obj.level ); endfunction
        function change_all_levels( obj, C ), obj.all_levels = C; endfunction
    endmethods
end

%% octave session
octave:1> E = Example('A', '.');
octave:2> E.get_level()
%> The level is A
octave:3> E.change_all_levels( {'this', 'should', 'not', 'work' } );
%> error: subsasgn: cannot assign constant property: all_levels
%> error: called from
%>    change_all_levels at line 25 column 66