Correct way to test if a value is a function?

Question

Geoff 2012-5-3

2
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/37374-correct-way-to-test-if-a-value-is-a-function

I'm using the following test to check if a value is a function (standard or anonymous):

if isa(value, 'function_handle')
  disp('Yeah bro');
else
  disp('Nah bro');
end

This satisfies me for everything I've thrown at it so far, and it's pleasing to have code that speaks my regional dialect... I just wanted to check that this is the accepted way to do it in MatLab.

I didn't see an equivalent function (as there is for ischar, iscell and the like) but that could be because it's not a very common thing to do.

Out of indulgent curiosity, is there a test to see if a function is anonymous or not? Forget about whether there's a real-world use case for it. I decided that this works:

if isa(value, 'function_handle')
  if strncmp(char(value), '@', 1)
    disp('Anonymous as, bro');
  else
    disp('Average as, bro');
  end
end

Obviously all this could be wrapped up into helpful little bundles devoid of Kiwi dialect...

isfun = @(f) isa(f, 'function_handle');
isstdfun = @(f) isfun(f) && ~strncmp(char(f), '@', 1);
isanonfun = @(f) isfun(f) && strncmp(char(f), '@', 1);

Anyone able to make this more concise? And is there an official word to describe functions declared with the function keyword? I kinda thought 'explicit' would suit.

Cheers =)

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per isakson 2012-5-4

I would replace char(f) by func2str(f), because it communicates the intent better. And the test strncmp(char(f), '@', 1) by strncmp( func2str(f), '@(', 2), because every(?) "string of a function_handle" starts with a "@".

Geoff 2012-5-7

I think the char() conversion does exactly that: sees I have passed a function handle and calls func2str(). Calling on one of my own file-defined functions, it does not prefix with @ (nor does it prefix built-in functions). But thank you for pointing out the correct function to use =)

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Answer 1

Sean de Wolski 2012-5-4

0
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在 MATLAB Online 中打开

To test if a function is defined in a file with the keyword function, test the output of exist().

v = exist('some_script') %v = 1;
v = exist('some_function') %v = 2

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Sean de Wolski 2012-5-8

Hi Geoff, This was just to answer the last question in your question suite:

"And is there an official word to describe functions declared with the function keyword? I kinda thought 'explicit' would suit"

Geoff 2012-5-11

Oh right... I was actually talking about a word, and not code. Being a programmer, I find it frustrating to have hazy or verbose descriptions of an established programming construct such as "function that is defined in a file as opposed to being in-built or anonymous". So I meant that if I was going to write code to separate these out: "is_anonymous_function", "is_matlab_function", "is_????_function", then what word would best fit the ????. Are you saying it should be 'script'?

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