Is there a version switch for codegen?

Is it possible to branch which part of the code is generated to C based on the current Matlab version, that is generating code at compile time?

For example I have a function which uses runtime recursion (which is only possible after R2016B) and an alternative without runtime recursion and I want to somehow switch between the factorial and the recursive line in the below simplified example based on the Matlab version generaing code from this function in order to make it backwards compatible with Matlab before R2016B.

function [x] = codertest(a)
	if verLessThan('matlab', '9.1')% starting with R2016B runtime recursion is allowed in code generation
	% some pragma like %#codegen or a function like coder.target is needed here to switch at compile time
		x = factorial(a);
	else
		x = recursive(a);
	end
end

function [rec] = recursive(x)
	if x == 1
		rec = x;
	else
		rec = x*recursive(x - 1);
	end
end

The file can be compiled with:

>> Tx = coder.typeof(1, [1, 1], [false, false]);
>> codegen('codertest.m', '-args', '{Tx}');

When I run these lines, Matlab before R2016B should therefore generate code using the "factorial" lines and Matlab after R2016B should use the "recursive" lines.

Simply using

coder.extrinsic('verLessThan');

does not solve the problem because this switches at runtime and then code generation will fail e.g. in R2015B with

??? Recursive calls are not allowed. Function 'recursive' participated in a recursive call.

which is exactly what I try to prevent.

Answer 1

[Ryan Livingston]

Use coder.const to forcibly constant fold the extrinsic call to verLessThan

if coder.const(verLessThan('matlab', '9.1'))
    % Older style code
else
    % Newer style code
end

The doc on this has more examples on constant folded extrinsic functions:

https://www.mathworks.com/help/coder/ref/coder.const.html

[Walter Roberson]

Ah, I had not encountered that before!

[Patrick Vogt]

Works perfectly, thank you.