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too-many-arguments (S902)

This rule is unstable and in preview. The --preview flag is required for use.

What it does

Checks for procedures with a large number of arguments.

Why is this bad?

Procedures with many arguments are harder to understand, maintain, call, and test. They often indicate that a procedure is doing too much and should be refactored into smaller, more focused procedures, or that a derived type should be used to group related arguments together.

For type-bound procedures, the first argument is not counted towards the total number of arguments. It is recommended to name this argument this or self to make it clear that the routine is type-bound, or else this rule may flag routines that are actually compliant.

As routines defined within interface blocks must match the procedure they are describing, they are exempt from this rule.

Example

The following procedure would be flagged for having too many arguments: 

subroutine update_position(x, y, z, vx, vy, vz, dt)
  real, intent(inout) :: x, y, z
  real, intent(in) :: vx, vy, vz, dt
  x = x + vx * dt
  y = y + vy * dt
  z = z + vz * dt
end subroutine update_position

Use instead: 

subroutine update_position(position, velocity, dt)
  type(vector), intent(inout) :: position
  type(vector), intent(in) :: velocity
  real, intent(in) :: dt
  position%x = position%x + velocity%x * dt
  position%y = position%y + velocity%y * dt
  position%z = position%z + velocity%z * dt
end subroutine update_position

where vector is a derived type defined as: 

type :: vector
 real :: x
 real :: y
 real :: z
end type vector

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