Programming and Data Types

Evaluating a Function Through Its Handle

Execute the target function of a function handle using the MATLAB feval command. The syntax for using this command with a function handle is

• feval(fhandle, arg1, arg2, ..., argn)
  

This acts similarly to a direct call to the function represented by fhandle, passing arguments arg1 through argn. The principal differences are:

• A function handle can be evaluated from within any function that you pass it to.
• The code source that MATLAB selects for evaluation depends upon which overloaded methods of the function were on the MATLAB path and in scope at the time the handle was constructed. (Argument types also affect method selection.) Path and scope are not considered at the time of evaluation.
• MATLAB does the work of initial function lookup at the time the function handle is constructed. This does not need to be done each time MATLAB evaluates the handle.

Note    The feval command does not operate on nonscalar function handles. Passing a nonscalar function handle to feval results in an error.

Function Evaluation and Overloading

To understand the relationship between function handles and overloading, it is helpful to review, briefly, the nature of MATLAB function calls. Because of overloading, it is useful to think of a single MATLAB function as comprising a number of code sources (for example, built-in code, M-files). When you call a MATLAB function without feval, the choice of which source is called depends upon two factors:

• The methods that are visible on the path at the time of the call
• The classes of the arguments to the function

MATLAB evaluates function handles in a similar manner. In most cases, a function handle represents a collection of methods that overload the function. When you evaluate a function handle using feval, the choice of the particular method called depends on:

• The methods that were visible on the path at the time the handle was constructed
• The classes of the arguments passed with the handle to the feval command

Constructing a Function Handle

Examples of Function Handle Evaluation