A System object™ is a specialized kind of MATLAB® object
that is optimized for iterative processing. Use System objects when
you need to call the
step method multiple times or
process data in a loop. When defining your own System object,
use the following suggestions to help your code run efficiently.
Define all one-time calculations in the
and cache the results in a private property. Use the
for repeated calculations.
If properties are accessed more than once in the
cache those properties as local variables inside the method. A typical
example of multiple property access is a loop. Iterative calculations
using cached local variables run faster than calculations that must
access the properties of an object. When the calculations for the
method complete, you can save the local cached results back to the
properties of that System object. Copy frequently used tunable
properties into private properties. This best practice also applies
In this example,
k is accessed multiple times
in each loop iteration, but is saved to the object property only once.
function y = stepImpl(obj,x) k = obj.MyProp; for p=1:100 y = k * x; k = k + 0.1; end obj.MyProp = k; end
Property default values are shared across all instances of an object. Two instances of a class can access the same default value if that property has not been overwritten by either instance.
Do not use string comparisons or string-based switch
statements in the
stepImpl method. Instead, create
a method handle in
setupImpl. This handle points
to a method in the same class definition file. Use that handle in
a loop in
This example shows how to use method handles and cached local
variables in a loop to implement an efficient object. In
on a string comparison and assign the method handle to the
Because there is a loop in
stepImpl, assign the
to a local method handle,
myFun, and then use
classdef MyClass < matlab.System function setupImpl(obj) if strcmp(obj.Method, 'Method1') obj.pMethodHandle = @myMethod1; else obj.pMethodHandle = @myMethod2; end end function y = stepImpl(obj,x) myFun = obj.pMethodHandle; for p=1:1000 y = myFun(obj,x) end end end function y = myMethod1(x) y = x+1; end function y = myMethod2(x) y = x-1; end end
If the number of System object inputs does not
change, do not implement the
Also do not implement the
when you explicitly list the inputs in the
instead of using
varargin. The same caveats apply
if you set the return argument from an object property, that object
property must have the
If the variables in a method do not need to retain their values between calls use local scope for those variables in that method.
For properties that do not change, define them in
have slower access times than
instead of the
public attribute for a property,
whenever possible. Some
public properties have
slower access times than
Avoid using customized
set methods, whenever possible.
Avoid using string comparisons within customized
set methods, whenever possible. Use
string comparisons instead.
Specify Boolean values using
For best practices for including System objects in code generation, see System Objects in MATLAB Code Generation.