change expect_silent to include object output

[r2evans]

(This is softly mentioned #614, and related to it since I'm trying to replace info functionality.)

I want to test for silence (or warning or error) from a function and still test its output. If a function is "expensive", I'd much rather not run it multiple times. However, the current expect_silent and family explicitly discard the object upon execution.

Right now I can do

expect_silent2 <- function(obj) { expect_silent(o <- obj) ; o ; }

but this does not work using the NSE hack for replacing info. That is:

expect_silent(myfunc(FALSE))
expect_silent(myfunc(TRUE))
# Error: myfunc(TRUE) produced warnings.
expect_silent2(myfunc(FALSE))
# [1] FALSE
expect_silent2(myfunc(TRUE))
# Error: o <- obj produced warnings.

That last error message isn't very useful, so I try the NSE trick:

expect_silent3 <- function(obj) { eval(bquote(expect_silent(.(o <- obj)))) ; o ; }
expect_silent3(myfunc(TRUE))
# Warning in myfunc(TRUE) : quux
# [1] TRUE

expect_silent4 <- function(obj) { eval(bquote(expect_silent(o <- .(obj)))) ; o ; }
expect_silent4(myfunc(TRUE))
# Warning in myfunc(TRUE) : quux
# [1] TRUE

expect_silent5 <- function(obj) eval(bquote(expect_silent2(.(obj))))
expect_silent5(myfunc(TRUE))
# Warning in myfunc(TRUE) : quux
# [1] TRUE

but none of them triggers the Error: myfunc(TRUE) produced warnings I would expect.

[hadley]

Just do the assignment inside the expectation:

expect_silent(x <- foo())
expect_equal(x, 10)

But you already know how to do that so I'm not sure what you want.I don't think it make sense for some expectation()

...

Ooooh, all the other expectations return the first object invisibly, so expect_silent() etc should be consistent.