coder.mustBeConst

Define an entry-point function testConstant that calls a local function local. The first input to the local function is validated to be a compile-time constant using the coder.mustBeConst validator.

function out = testConst(in1,in2)
if in1 > 0
    out = local(in1,in2);
else
    out = local(-in1,in2);
end
end

function u = local(x,y)
arguments
    x {coder.mustBeConst}
    y 
end
u = sqrt(x) + y;
end

Generate code for the testConst function using the codegen command. Specify the entry-point inputs in1 and in2 to be scalar doubles using the -args option.

codegen testConst -args {0,0}

Value must be constant.

Error in ==> testConst Line: 11 Column: 8
Code generation failed: View Error Report

Code generation fails because the absolute value of the run-time input in1 is directly passed as the first argument when calling the function local. Because this value is not known at compile time, the coder.mustBeConst validator throws an error during code generation.

Modify the codegen command by specifying the first entry-point input to be of a constant type using the coder.Constant (MATLAB Coder) function.

codegen testConst -args {coder.Constant(0),0}

Code generation successful.

Because the first input passed to local is of a constant type, the coder.mustBeConst validator does not throw an error and code generation succeeds.