Improve output of userdata, handling__tostring and NULL
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When interpreting userdata values using 'inspect', the numeric identifiers are useful to match identify of pointers (comparing the low counters like `<userdata 3> is easier than reading long pointers like `userdata: 0x749abc39efa29`). However, the `NULL` pointer is enough of a special case that it is important to know when one of those numbered pointers happens to be `NULL`. When one is dealing with things like JSON parsers, where the only usual userdata is `cjson.null`, one gets accostumed over time to interpret `<userdata 1>` to mean `NULL`. This is not obvious, however, and a seasoned user will trip up the day another userdata is used in the same table and `NULL` is now `<userdata 2>`. Adding a test for this would require compiling and loading a C extension.
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This PR includes 2 commits:
The first one includes evaluation of
__tostringfor userdata values. This should be safe because__tostringof userdata is unlikely to recurse intoinspect. A test is included.The second one adds a special case for NULL userdata.
When interpreting userdata values using 'inspect', the numeric identifiers
are useful to match identify of pointers (comparing the low counters
like
<userdata 3> is easier than reading long pointers likeuserdata: 0x749abc39efa29`).However, the
NULLpointer is enough of a special case that it isimportant to know when one of those numbered pointers happens to
be
NULL. When one is dealing with things like JSON parsers, wherethe only usual userdata is
cjson.null, one gets accostumed overtime to interpret
<userdata 1>to meanNULL. This is not obvious,however, and a seasoned user will trip up the day another userdata
is used in the same table and
NULLis now<userdata 2>.Adding a test for this would require compiling and loading a C extension, such as
lua-cjson. I can do so if desired.