From a string to function handle of a function handle

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Patrick Mboma
Patrick Mboma 2017-7-19
评论： James Tursa 2017-7-20
Hi,
Is it possible to transform a string into a function handle calling another function handle?
More specifically, consider the following simple example
func1=@(x)mean(x)
tmp='@(x)func1(x)+3'
we know that defining
func2=str2func(tmp)
does not work.
Is there any way to create a function handle using tmp that will work?
Thanks

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采纳的回答

James Tursa
James Tursa 2017-7-19
func2 = eval(tmp);
  2 个评论
James Tursa
James Tursa 2017-7-20
Yep, agreed. If you don't know where that string is coming from and what could be in it or don't trust the source, then eval should probably be avoided.

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更多回答（1 个）

Walter Roberson
Walter Roberson 2017-7-19
tmp='@(x)feval(evalin(''caller'',''func1''),x)+3'
  2 个评论
Patrick Mboma
Patrick Mboma 2017-7-19
Thanks Walter, I guess this would work but at the same time it looks like a very cumbersome way of going about it especially if you have long expressions.
Walter Roberson
Walter Roberson 2017-7-19
The basic issue is that str2func() is operating in a context outside your current workspace, so it does not have access to any variables in your workspace. evalin('caller') gives it that access. You would have the same difficulty with a plain variable:
>> A = 5
A =
5
>> tmp = '@(x) x+A'
tmp =
'@(x) x+A'
>> func2 = str2func(tmp)
func2 =
function_handle with value:
@(x)x+A
>> func2(7)
Undefined function or variable 'A'.
Error in @(x)x+A
str2func always does textual substitutions.

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