Support `undef` for `mrb_ary_splice()` instead of `[]`
When removing elements from an array, it is possible to avoid creating
an empty array.
Before this patch:
```c
mrb_ary_splice(mrb, ary, head, len, mrb_ary_new(mrb));
```
After this patch:
```c
mrb_ary_splice(mrb, ary, head, len, mrb_undef_value());
```
MODIFY
include/mruby/array.h
include/mruby/array.h
@@ -239,6 +239,7 @@ MRB_API mrb_value mrb_ary_entry(mrb_value ary, mrb_int offset);
* @param head Beginning position of a replacement subsequence.
* @param len Length of a replacement subsequence.
* @param rpl The array of replacement elements.
+ * It is possible to pass `mrb_undef_value()` instead of an empty array.
* @return The receiver array.
*/
MRB_API mrb_value mrb_ary_splice(mrb_state *mrb, mrb_value self, mrb_int head, mrb_int len, mrb_value rpl);

MODIFY
src/array.c
src/array.c
@@ -732,6 +732,10 @@ mrb_ary_splice(mrb_state *mrb, mrb_value ary, mrb_int head, mrb_int len, mrb_val
argv = ARY_PTR(r);
}
}
+ else if (mrb_undef_p(rpl)) {
+ argc = 0;
+ argv = NULL;
+ }
else {
argc = 1;
argv = &rpl;

Support `undef` for `mrb_ary_splice()` instead of `[]`

When removing elements from an array, it is possible to avoid creating
an empty array.

Before this patch:

```c
mrb_ary_splice(mrb, ary, head, len, mrb_ary_new(mrb));
```

After this patch:

```c
mrb_ary_splice(mrb, ary, head, len, mrb_undef_value());
```