Extend expect_length to use an S4 object's length method, if exists #564
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hadley
reviewed
Oct 1, 2017
R/expect-length.R
Outdated
| @@ -15,8 +15,8 @@ expect_length <- function(object, n) { | |||
| stopifnot(is.numeric(n), length(n) == 1) | |||
| lab <- label(object) | |||
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| if (!is_vector(object)) { | |||
| fail(sprintf("%s is not a vector.", lab)) | |||
| if (!has_length(object)) { | |||
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I'd rather simply remove this check all together. Would you mind doing that?
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Check removed. |
hadley
reviewed
Oct 2, 2017
tests/testthat/test-expect-length.R
Outdated
| # Default for S4 objects that don't inherit a length method: always length 1 | ||
| expect_success(expect_length(A(x=1:5, y=3), 1)) | ||
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| # B does has a length method defined |
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This mostly tests of the implementation of length(). I think you only need the test for ExpectLengthB
hadley
approved these changes
Oct 2, 2017
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Thanks! |
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No, thank you! |
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expect_lengthis a clean, convenient shortcut forexpect_equal(length(x), n), but in its current implementation, only objects that are one of R's internal array types are whitelisted. An S4 object that doesn't inherit from one of those types is forbidden, even if it has alengthmethod defined. Aside from the inconvenience of having to fall back toexpect_equal, this limitation increases the chances of writing a misleading test because, as?lengthsays, "[a]ll other objects (including functions) have length one."This pull request extends
expect_lengthto work with S4 objects that have a length method. The additional check examines whetherselectMethodselects the default.Primitive("length")(which always returns 1) for an S4 object. If a length method other than the primitive is set or inherited,expect_lengthwill proceed. Other seemingly more natural ways of checking for the existence of a method don't work:existsMethoddoesn't follow inheritance andhasMethodalways returnsTRUEfor S4 objects because the primitive method is found.This pull request also contains a commit that updates the junit test fixture for what I am guessing is a change in the 'xml2' package. When I reset my fork to upstream/master, it failed on Travis. I suspect an 'xml2' change caused the failure because the most recent release of that package was after the most recent commit to the master branch of 'testthat'.