force                  package:base                  R Documentation

_F_o_r_c_e _e_v_a_l_u_a_t_i_o_n _o_f _a_n _A_r_g_u_m_e_n_t

_D_e_s_c_r_i_p_t_i_o_n:

     Forces the evaluation of a function argument.

_U_s_a_g_e:

     force(x)

_A_r_g_u_m_e_n_t_s:

       x: a formal argument.

_D_e_t_a_i_l_s:

     'force' forces the evaluation of a formal argument.  This can be
     useful if the argument will be captured in a closure by the
     lexical scoping rules and will later be altered by an explicit
     assignment or an implicit assignment in a loop or an apply
     function.

_N_o_t_e:

     'force' does not force the evaluation of promises.

_E_x_a_m_p_l_e_s:

     f <- function(y) function() y
     lf <- vector("list", 5)
     for (i in seq(along = lf)) lf[[i]] <- f(i)
     lf[[1]]()  # returns 5

     g <- function(y) { force(y); function() y }
     lg <- vector("list", 5)
     for (i in seq(along = lg)) lg[[i]] <- g(i)
     lg[[1]]()  # returns 1

