Take list name from property name

Fixes #371

NEWS.md

@@ -1,5 +1,8 @@
 # S7 (development version)
 
+* In `new_class()`, properties can either be named by naming the element
+  of the list or by supplying the `name` argument to `new_property()` (#371).
+
 * S7 provides a new automatic backward compatibility mechanism to provide
   a version of `@` that works in R before version 4.3 (#326).
 

R/property.R

@@ -393,7 +393,7 @@ as_properties <- function(x) {
   }
 
   out <- Map(as_property, x, names2(x), seq_along(x))
-  names(out) <- names2(x)
+  names(out) <- vapply(out, function(x) x$name, FUN.VALUE = character(1))
 
   if (anyDuplicated(names(out))) {
     stop("`properties` names must be unique", call. = FALSE)
@@ -403,15 +403,22 @@ as_properties <- function(x) {
 }
 
 as_property <- function(x, name, i) {
-  if (name == "") {
-    msg <- sprintf("`property[[%i]]` is missing a name", i)
-    stop(msg, call. = FALSE)
-  }
 
   if (is_property(x)) {
-    x$name <- name
+    if (is.null(x$name)) {
+      if (name == "") {
+        msg <- sprintf("`property[[%i]]` must have a name or be named.", i)
+        stop(msg, call. = FALSE)
+      }
+      x$name <- name
+    }
     x
   } else {
+    if (name == "") {
+      msg <- sprintf("`property[[%i]]` must be named.", i)
+      stop(msg, call. = FALSE)
+    }
+
     class <- as_class(x, arg = paste0("property$", name))
     new_property(x, name = name)
   }

tests/testthat/_snaps/property.md

@@ -160,12 +160,12 @@
       as_properties(list(1))
     Condition
       Error:
-      ! `property[[1]]` is missing a name
+      ! `property[[1]]` must be named.
     Code
       as_properties(list(new_property(class_character)))
     Condition
       Error:
-      ! `property[[1]]` is missing a name
+      ! `property[[1]]` must have a name or be named.
     Code
       as_properties(list(x = 1))
     Condition

tests/testthat/test-property.R

@@ -287,6 +287,10 @@ test_that("as_properties normalises properties", {
     as_properties(list(x = new_property(class = class_numeric))),
     list(x = new_property(class_numeric, name = "x")
   ))
+  expect_equal(
+    as_properties(list(new_property(name = "y"))),
+    list(y = new_property(name = "y")
+  ))
 })
 
 test_that("as_properties() gives useful error messages", {