Can anyone explain how can this happen?

function myfunctest
  subfcn_set('notafunc');
  whos
  which notafunc
  notafunc
  subfcn_set('sin');
  whos
  which sin
  sin
end

function subfcn_set(n)
  assignin('caller', n, ['I am ',n]);
end

running myfunctest in matlab gives

>> myfunctest
  Name          Size            Bytes  Class    Attributes

    notafunc      1x13               26  char               

notafunc is a variable.

notafunc =

I am notafunc

    Name          Size            Bytes  Class    Attributes

    notafunc      1x13               26  char               
    sin           1x8                16  char               

sin is a variable.
Error using sin
Not enough input arguments.

Error in myfunctest (line 13)
sin

The builtin sin function is called even when a local variable "sin" exists.

Answer 1

[Ray Lee]

I found the doc.

http://www.mathworks.com/help/matlab/matlab_prog/variable-names.html#btcg64o-1

Another potential source of name conflicts occurs when you define a function that calls load or eval (or similar functions) to add variables to the workspace. In some cases, load or eval add variables that have the same names as functions. Unless these variables are in the function workspace before the call to load or eval, the MATLAB parser interprets the variable names as function names.

[Guillaume]

Of course, the advice to avoid creating variables with the same name as a function is not really useful since the names of existing functions depends on which toolbox you have and whichever code is in your path.

If only matlab had a proper namespace system...

[Ray Lee]

+1 for Guillaume's comment

Answer 2

[Guillaume]

If you put a breakpoint on the sin line and execute it from the debugger the error does not occur, so I suspect it's a 'bug' with the Just-In-Time compiler introduced recently. I assume that when it loads the function, the JIT compiler sees that there is no sin variable created in the function so assumes that sin is a function call.

While it's a bug, it's also another reason for avoiding dynamic variable creation using eval, assignin, and their ilk.