All chart constructors in the package return an object of class
shewhart_chart with a more specific subclass (shewhart_i_mr,
shewhart_xbar_r, shewhart_p, shewhart_regression, ...). The
shared slots are type, augmented, limits, violations, fits,
rules, sigma_hat, sigma_method, phase, n, call, and
metadata. is_shewhart_chart() tests inheritance.
Examples
fit <- shewhart_i_mr(data.frame(v = rnorm(30)), v)
is_shewhart_chart(fit)
#> [1] TRUE