If I use the inline
function in MATLAB I can create a single function name that could respond differently depending on previous choices:
if (someCondition)
p = inline('a - b','a','b');
else
p = inline('a + b','a','b');
end
c = p(1,2);
d = p(3,4);
But the inline functions I'm creating are becoming quite epic, so I'd like to change them to other types of functions (i.e. m-files, subfunctions, or nested functions).
Let's say I have m-files like Mercator.m
, KavrayskiyVII.m
, etc. (all taking a value for phi
and lambda
), and I'd like to assign the chosen function to p
in the same way as I have above so that I can call it many times (with variable sized matrices and things that make using eval
either impossible or a total mess).
I have a variable, type
, that will be one of the names of the functions required (e.g. 'Mercator'
, 'KavrayskiyVII'
, etc.). I figure I need to make p
into a pointer to the function named inside the type
variable. Any ideas how I can do this?
Use the str2func
function (assumes the string in type
is the same as the name of the function):
p = str2func(type); % Create function handle using function name
c = p(phi, lambda); % Invoke function handle
NOTE: The documentation mentions these limitations:
Function handles created using
str2func
do not have access to variables outside of their local workspace or to nested functions. If your function handle contains these variables or functions, MATLAB® throws an error when you invoke the handle.
Use a SWITCH statement and function handles:
switch type
case 'Mercator'
p = @Mercator;
case 'KavrayskiyVII'
p = @KavrayskiyVII;
... % Add other cases as needed
end
c = p(phi, lambda); % Invoke function handle
Use EVAL and function handles (suggested by Andrew Janke):
p = eval(['@' type]); % Concatenate string name with '@' and evaluate
c = p(phi, lambda); % Invoke function handle
As Andrew points out, this avoids the limitations of str2func
and the extra maintenance associated with a switch statement.