Allow cast era_yr -> character. Closes #11

But not character -> era_yr for now, see # 38

NAMESPACE

@@ -11,8 +11,10 @@ S3method(vec_arith.era_yr,default)
 S3method(vec_arith.era_yr,era_yr)
 S3method(vec_arith.era_yr,numeric)
 S3method(vec_arith.numeric,era_yr)
+S3method(vec_cast,character.era_yr)
 S3method(vec_cast,double.era_yr)
 S3method(vec_cast,era.era)
+S3method(vec_cast,era_yr.character)
 S3method(vec_cast,era_yr.double)
 S3method(vec_cast,era_yr.era_yr)
 S3method(vec_cast,era_yr.integer)

NEWS.md

@@ -5,6 +5,7 @@
 * More precise epoch value for Nowruz (Solar Hijri) eras: `621.2218` instead of `622`.
 * `this_year()` now considers the current date, returns a floored integer (i.e. the actual current calendar year), and is vectorised over `era`.
 * Class constructors `era()` and `yr()` return a zero-length vector when called with no arguments (instead of an error), allowing them to be used as [prototypes](https://vctrs.r-lib.org/articles/type-size.html)
+* `era_yr` objects can be cast to character vectors (e.g. `as.character(yr(1, "BP"))`)
 
 # era 0.3.1
 

R/s3-yr.R

@@ -200,6 +200,16 @@ vec_cast.era_yr.double <- function(x, to, ...) {
   new_yr(x, yr_era(to))
 }
 
+#' @export
+vec_cast.character.era_yr <- function(x, to, ...) {
+  paste(vec_data(x), era_label(yr_era(x)))
+}
+
+#' @export
+vec_cast.era_yr.character <- function(x, to, ...,  x_arg = "", to_arg = "") {
+  stop_incompatible_cast(x, to, x_arg = x_arg, to_arg = to_arg)
+}
+
 # Format/print ---------------------------------------------------------
 #' @export
 vec_ptype_full.era_yr <- function(x, ...) {

tests/testthat/test-yr.R

@@ -74,6 +74,15 @@ test_that("era_yr cast methods return correct class", {
   # double <-> era_yr
   expect_type(vec_cast(new_yr(), double()), "double")
   expect_s3_class(vec_cast(double(), new_yr()), "era_yr")
+
+  # character <-> era_yr
+  expect_type(vec_cast(new_yr(), character()), "character")
+  expect_error(vec_cast(character(), new_yr()),
+               class = "vctrs_error_incompatible_type")
+})
+
+test_that("casting era_yr to character returns expected output", {
+  expect_equal(vec_cast(yr(1:3, "BP"), character()), c("1 BP", "2 BP", "3 BP"))
 })
 
 test_that("format.era_yr returns expected output", {