library-mirrors/inspect.lua
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add a special case for NULL userdata

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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.
This commit is contained in:
Hisham Muhammad 2019-04-05 16:59:40 -03:00
parent 6e7f2dce9b
commit c32cdda2bb
1 changed files with 8 additions and 1 deletions
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9
inspect.lua
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@ -309,9 +309,16 @@ function Inspector:putValue(v)
elseif tv == 'userdata' then
local mt = getmetatable(v)
local toStringResult = mt and getToStringResultSafely(v, mt)
self:puts('<', tv, ' ', self:getId(v), '>')
if toStringResult then
self:puts('<userdata ', self:getId(v), '>')
self:puts(' -- ', escape(toStringResult))
else
local str = tostring(v)
if str == "userdata: NULL" then
self:puts('<userdata NULL>')
else
self:puts('<userdata ', self:getId(v), '>')
end
end
else
self:puts('<', tv, ' ', self:getId(v), '>')