Programming

Additional Information on Function Handles

This section covers the following topics:

• Maximum Length of a Function Name
• How MATLAB Constructs a Function Handle
• Saving and Loading Function Handles

Maximum Length of a Function Name

Function names used in handles are unique up to N characters, where N is the number returned by the function namelengthmax. If the function name exceeds that length, MATLAB truncates the latter part of the name.

For function handles created for Java constructors, the length of any segment of the package name or class name must not exceed namelengthmax characters. (The term segment refers to any portion of the name that lies before, between, or after a dot. For example, java.lang.String has three segments). The overall length of the string specifying the package and class has no limit.

How MATLAB Constructs a Function Handle

At the time you create a function handle, MATLAB maps the handle to one or more implementations of the function specified in the constructor statement:

• fhandle = @functionname
  

In selecting which function(s) to map to, MATLAB considers

• Scope -- The function named must be on the MATLAB path at the time the handle is constructed.
• Precedence -- MATLAB selects which function(s) to map to according to the function precedence rules described under How MATLAB Determines Which Method to Call.
• Overloading -- If additional M-files on the path overload the function for any of the standard MATLAB data types, such as double or char, then MATLAB maps the handle to these M-files as well.

M-files that overload a function for classes outside of the standard MATLAB data types are not mapped to the function handle at the time it is constructed. Function handles do operate on these types of overloaded functions, but MATLAB determines which implementation to call at the time of evaluation in this case.

Saving and Loading Function Handles

You can save and load function handles in a MAT-file using the MATLAB save and load functions. If you load a function handle that you saved in an earlier MATLAB session, the following conditions could cause unexpected behavior:

• Any of the M-files that define the function have been moved, and thus no longer exist on the path stored in the handle.
• You load the function handle into an environment different from that in which it was saved. For example, the source for the function either doesn't exist or is located in a different directory than on the system on which the handle was saved.

In both of these cases, the function handle is now invalid because it no longer maps to any existing function code. Although the handle is invalid, MATLAB still performs the load successfully and without displaying a warning. Attempting to invoke the handle, however, results in an error.

Function Handles

Calling Functions

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