Re: Testing for function handles

[John W. Eaton]

On  9-Nov-2011, Richard Crozier wrote:

| 
| 
| On 09/11/2011 11:15, Richard wrote:
| > On 09/11/2011 10:32, Juan Pablo Carbajal wrote:
| >> On Wed, Nov 9, 2011 at 11:01 AM, Richard<address@hidden>  wrote:
| >>> On 09/11/2011 08:18, Dr. Alexander Klein wrote:
| >>>> Good morning,
| >>>>
| >>>> is there any preferred way to check whether a given parameter or
| >>>> variable
| >>>> contains a function handle?
| >>>>
| >>>> I find myself strcmp'ing the result of typeinfo quite often, but
| >>>> this is
| >>>> really clumsy. Then again, ishandle only checks for graphics handles
| >>>> ...
| >>>>
| >>>> Best regards,
| >>>>
| >>>>         Alex
| >>>>
| >>> if it is octave code you can use the 'isa' function e.g.
| >>>
| >>> isa(@sin, 'function_handle')
| >>>
| >>> but maybe I'm misunderstanding and you mean in the C++ sources or
| >>> something.
| >>>
| >>> Richard
| >>>
| >>> -- 
| >>> The University of Edinburgh is a charitable body, registered in
| >>> Scotland, with registration number SC005336.
| >>>
| >>>
| >> Checking
| >> f = @(x)x;
| >> n=5e4;
| >> t0=cputime;
| >> for i=1:n
| >>    strcmp(typeinfo(f),'function_handle');
| >> end
| >> t=cputime-t0
| >>
| >> t0=cputime;
| >> for i=1:n
| >>    isa(f,'function_handle');
| >> end
| >> t=cputime-t0
| >>
| >> I get
| >> t =  1.0521
| >> for strcmp
| >> t =  5.0083
| >> for isa
| >>
| >> Is the benchmark correct?
| >>
| > 
| > Yes, well on my machine:
| > 
| > f = @(x)x;
| > n=5e4;
| > tic;
| > for i=1:n
| >   strcmp(typeinfo(f),'function_handle');
| > end
| > toc
| > 
| > tic;
| > for i=1:n
| >   isa(f,'function_handle');
| > end
| > toc
| > 
| > Yields
| > 
| > Elapsed time is 0.862049 seconds.
| > Elapsed time is 3.15218 seconds.
| > octave-3.2.4.exe:3>
| > 
| > Although as you can see I'm using an out of date version of Octave
| > 
| > Not sure why this should be so though, but maybe this is why isa is so
| > sparsely documented?
| > 
| > 
| 
| Incidentally the following in Matlab
| 
| f = @(x)x;
| n=5e4;
| 
| tic;
| for i=1:n
|   isa(f,'function_handle');
| end
| toc
| 
| Returns (on a different, less powerful, machine):
| 
| Elapsed time is 0.249872 seconds.
| 
| On Matlab, isa is not an mfile though. There is also no typeinfo in
| Matlab (R2008a at least) for comparison.

Try class instead of typeinfo.

Yes, we could add an is_function_handle that could be faster than
isa.  Would someone like to submit a changeset for that?

Look at isa.m ("type isa" at the Octave prompt) and you'll see that it
is more complicated than just strcmp (class (x), classname) because it
has to be able to do things like 'isa (x, "float")'.

Also, why is this thread here instead of the help list?

jwe