x[, a := v] on a parameter x, which changes the table the caller hands over in place
assign(x, value, envir)
get(x, envir) and exists(x, envir)
rm(list = x, envir)
env$x <- value and env[["x"]] <- value, which define in what env holds only if that is an environment, a list they copy
What a call does to the variable it names in an environment.