data <- tibble::tibble(x = 1:3, y = 3:1)
tibble::add_column(data, z = -1:1, w = 0)
add_missing_column(data, z = -1:1, .before = "y")
# add_column errors if already present
try(tibble::add_column(data, x = 4:6))
# add_missing_column silently ignores
add_missing_column(data, x = 4:6)
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