Matlab subsref: {} with string argument doesn't work, why?

Question

The Mathworks File Exchange repository has several hash or dictionary class implementations. Everything I examined uses parenthesis overloading to refer to keywords, for example.

d = Dict;
d('foo') = 'bar';
y = d('foo');

which seems like a reasonable interface. It would be preferable, however, if you want to easily have dictionaries that contain other dictionaries, use brackets {}instead of parentheses, since this circumvents the restriction on the type of MATLAB syntax (arbitrary, apparently), which does not have multiple parentheses, but multiple braces are allowed, i.e.

t{1}{2}{3}  % is legal MATLAB
t(1)(2)(3)  % is not legal MATLAB

So, if you want to easily insert dictionaries into dictionaries,

dict{'key1'}{'key2'}{'key3'}

Perl, , Python, , n-1 n , . subsref subsasgn , {}, (), .

, .

. ( . , , , .)

classdef TestBraces < handle

    properties
        % not a full hash table implementation, obviously
        key
        value
    end

    methods(Access = public)


        function val = subsref(obj, ref)
            % Re-implement dot referencing for methods.
            if strcmp(ref(1).type, '.')
                % User trying to access a method             
                % Methods access
                if ismember(ref(1).subs, methods(obj))
                    if length(ref) > 1
                        % Call with args
                        val = obj.(ref(1).subs)(ref(2).subs{:});
                    else
                        % No args
                        val = obj.(ref.subs);
                    end
                    return;
                end                
                % User trying to access something else.
                error(['Reference to non-existant property or method ''' ref.subs '''']);
            end
            switch ref.type
                case '()'
                    error('() indexing not supported.');
                case '{}'
                    theKey = ref.subs{1};
                    if isequal(obj.key, theKey)
                        val = obj.value;
                    else
                        error('key %s not found', theKey);
                    end
                otherwise
                    error('Should never happen')
            end
        end    

        function obj = subsasgn(obj, ref, value)
            %Dict/SUBSASGN  Subscript assignment for Dict objects.
            %
            %  See also: Dict
            %

            if ~strcmp(ref.type,'{}')
                error('() and dot indexing for assignment not supported.');
            end

            % Vectorized calls not supported
            if length(ref.subs) > 1
                error('Dict only supports storing key/value pairs one at a time.');
            end
            theKey = ref.subs{1};
            obj.key = theKey;
            obj.value = value;
        end % subsasgn        
    end     
end

, :

t = TestBraces;
t{'foo'} = 'bar'

( , t.) , subsasgn .

(subsref ):

t{'foo'}
??? Error using ==> subsref
Too many output arguments.

, subsref , , , MATLAB, .

() , , () {}. ( , , .)

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Answer 1

, :

function n = numel(obj, varargin)
    n = 1;
end

EDIT: .

, subsref, varargout - ​​ . , , :

>> c = {1,2,3,4,5};
>> [a,b,c] = c{[1 3 5]}
a =
     1
b =
     3
c =
     5

subsref . 3, .

, :

t{'foo'}

? 3. MATLAB , . , - 3, subsref . , . , , , MATLAB , numel. doc:

numel subsref subsasgn. subsref ( ), numel (nargout), subsref. subsasgn, numel (), subsasgn. subsasgn - , numel plus 2 ( ).

, , n, numel . n nargout subsref subsasgn , numel, n, "subsref" "subsasgn". MATLAB .

.