R : confusion regarding LHS and RHS of assignment and order of operation -

i having fundamental confusion r. have snippet of r code.

> m <- 1:10 > m  [1]  1  2  3  4  5  6  7  8  9 10 > dim(m) <- c(2,5) > m      [,1] [,2] [,3] [,4] [,5] [1,]    1    3    5    7    9 [2,]    2    4    6    8   10 

now c/python programmer , line dim(m) <- c(2,5) incredibly confusing me. realize changed vector matrix, looking @ not understand logic/order of operation.

<- assignment operator in r. me, logically order of operation : assign (2,5) output of dim(m). since output of dim(m) isn't assigned variable, output lost.

could explain how should read line dim(m) <- c(2,5)? order of operation? seems order of operation using <- changes depending on lhs and rhs of equation.

these special functions called replacement functions. quote hadley's advanced-r book:

replacement functions act modify arguments in place, , have special name xxx<-. typically have 2 arguments (x , value), although can have more, , must return modified object. example, following function allows modify second element of vector:

`second<-` <- function(x, value) {   x[2] <- value   x } x <- 1:10 second(x) <- 5l x #>  [1]  1  5  3  4  5  6  7  8  9 10 

when r evaluates assignment second(x) <- 5, notices left hand side of <- not simple name, looks function named second<- replacement.

you can check full chapter here under replacement functions title.