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program assertion_examples
!! Demonstrate the use of assertions as runtime checks on the satisfaction of
!! of two kinds of constraints:
!! 1. Preconditions: requirements for correct execution at the start of a procedure and
!! 2. Postconditions: requirements for correct execution at the end of a procedure.
use assert_m, only : assert
implicit none
print *, "roots: ", roots(a=1.,b=0.,c=-4.)
contains
pure function roots(a,b,c) result(zeros)
!! Calculate the roots of a quadratic polynomial
real, intent(in) :: a, b, c
real, allocatable :: zeros(:)
real, parameter :: tolerance = 1E-06
associate(discriminant => b**2 - 4*a*c)
call assert(assertion = discriminant >= 0., description = "discriminant >= 0") ! precondition
allocate(zeros(2))
! there's a deliberate math bug in the following line, to help demonstrate assertion failure
zeros = -b + [sqrt(discriminant), -sqrt(discriminant)]
end associate
! This assertion will fail (due to the defect above) when ASSERTIONS are enabled:
call assert(all(abs(a*zeros**2 + b*zeros + c) < tolerance), "All residuals within tolerance.") ! postcondition
end function
end program
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