Matlab Codegen: Does not support anonymous functions

Question

I am attempting to change some Matlab code into C++ however when I use %#codegen the error "Code generation does not support anonymous functions" appears next to vec = @(x) x(:); . Below is the Matlab function. What can I change to remove this error?

    function [L,num,sz] = label(I,n) %#codegen

    % Check input arguments
    error(nargchk(1,2,nargin));
    if nargin==1, n=8; end

    assert(ndims(I)==2,'The input I must be a 2-D array')

    sizI = size(I);
    id = reshape(1:prod(sizI),sizI);
    sz = ones(sizI);

    % Indexes of the adjacent pixels
    vec = @(x) x(:);
    if n==4 % 4-connected neighborhood
    idx1 = [vec(id(:,1:end-1)); vec(id(1:end-1,:))];
    idx2 = [vec(id(:,2:end)); vec(id(2:end,:))];
    elseif n==8 % 8-connected neighborhood
    idx1 = [vec(id(:,1:end-1)); vec(id(1:end-1,:))];
    idx2 = [vec(id(:,2:end)); vec(id(2:end,:))];
    idx1 = [idx1; vec(id(1:end-1,1:end-1)); vec(id(2:end,1:end-1))];
    idx2 = [idx2; vec(id(2:end,2:end)); vec(id(1:end-1,2:end))];
    else
    error('The second input argument must be either 4 or 8.')
    end

    % Create the groups and merge them (Union/Find Algorithm)
   for k = 1:length(idx1)
   root1 = idx1(k);
   root2 = idx2(k);

   while root1~=id(root1)
    id(root1) = id(id(root1));
    root1 = id(root1);
   end
   while root2~=id(root2)
    id(root2) = id(id(root2));
    root2 = id(root2);
   end

   if root1==root2, continue, end
   % (The two pixels belong to the same group)

   N1 = sz(root1); % size of the group belonging to root1
   N2 = sz(root2); % size of the group belonging to root2

   if I(root1)==I(root2) % then merge the two groups
    if N1 < N2
        id(root1) = root2;
        sz(root2) = N1+N2;
    else
        id(root2) = root1;
        sz(root1) = N1+N2;
    end
    end
    end

    while 1
    id0 = id;
    id = id(id);
    if isequal(id0,id), break, end
    end
    sz = sz(id);

    % Label matrix
    isNaNI = isnan(I);
    id(isNaNI) = NaN;
    [id,m,n] = unique(id);
    I = 1:length(id);
    L = reshape(I(n),sizI);
    L(isNaNI) = 0;

    if nargout>1, num = nnz(~isnan(id)); end 

Answer 1

You can use following function and comment the anonymous function

function x=vec( id )
    x = id(:);
end

This basically does same what your anonymous is achieving

Answer 2

MATLAB Coder supports anonymous functions since R2016b. The above example works with the latest version of MATLAB Coder (checked 11/30/2021).