Re: [ANN] Lua 5.4.0 (work1) now available
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- Subject: Re: [ANN] Lua 5.4.0 (work1) now available
- From: Roberto Ierusalimschy <roberto@...>
- Date: 2018年3月14日 11:09:34 -0300
> > t[i]=undef is a special syntax form that means "remove the key 'i'
> > from table 't'".
>
> But it seems like an assignment. Wouldn't be better to create a special
> syntax for removing a key from a table instead pretending it as an
> assingment?
>
> You should have considered a pair of functions, such as table.undefine(t,
> i) to undefine a key, and table.defined(t, i) to check whether the table
> has the key. Why did you choose the assignment?
Mainly because of compatibility with older versions. As I said, I like
the idea of using 't[i]=undef' even in older versions, as a idiom to
better document things being removed from a table.
We fully agree that it may be confusing; that is why we are testing it
in this work release.
A new syntax (such as "delete a[k]" or anything like that) would be
the worst for compatibility, as new programs using it would not even
compile in older Lua. Functions are not that bad; with something
like
table.undefine = table.undefine or function(t,k) t[k] = nil end
we get compatibility in older Lua. But with 't[i=undef' we have
compatibility without any work :-)
-- Roberto