Add `mrb_get_arg1()` that retrieves single (and only) argument.

`mrb_get_arg1()` raises `ArgumentError` if the method does not receive one
argument.

And replaces all `mrb_get_args(mrb, "o", &arg)` by the new function.

1 files changed, 13 insertions, 0 deletions

diff --git a/include/mruby.h b/include/mruby.h
index fef4a0d47..5aba2934a 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -959,8 +959,21 @@ mrb_get_mid(mrb_state *mrb) /* get method symbol */
  */
 MRB_API mrb_int mrb_get_argc(mrb_state *mrb);
 
+/**
+ * Retrieve an array of arguments from mrb_state.
+ *
+ * Correctly handles *splat arguments.
+ */
 MRB_API mrb_value* mrb_get_argv(mrb_state *mrb);
 
+/**
+ * Retrieve the first and only argument from mrb_state.
+ * Raises ArgumentError unless the number of arguments is exactly one.
+ *
+ * Correctly handles *splat arguments.
+ */
+MRB_API mrb_value mrb_get_arg1(mrb_state *mrb);
+
 /* `strlen` for character string literals (use with caution or `strlen` instead)
     Adjacent string literals are concatenated in C/C++ in translation phase 6.
     If `lit` is not one, the compiler will report a syntax error: