Re: { 1 } [1] vs ( { 1 } ) [1]
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- Subject: Re: { 1 } [1] vs ( { 1 } ) [1]
- From: Roberto Ierusalimschy <roberto@...>
- Date: 2021年1月14日 16:30:51 -0300
> Using Lua 5.3.
>
> Code:
>
> return { 1 } [1]
>
> Result:
>
> <eof> expected near '['
>
> Code:
>
> return ( { 1 } ) [1]
>
> Result:
>
> 1
>
> The question is, why is the first version not accepted? I am not
> asking for an explanation why the details are such and such, but
> rather for a rationale, if there is one, that a table "literal"
> (constructor) should not appear in some expressions unless it is
> wrapped in parentheses.
For regularity, what can come before [exp] is the same stuff that
can come before (explist), forming function calls. Allowing {1}[1]
would also allow {1}(1), which being a function call could be
used as a statement:
a = b
{1}(1) -- "calling" table {1}
That would create another ambiguity in the grammar, similar to the
(already present) ambiguity with parentheses:
a = b
(print)(1) -- calling print or calling b?
We chose to reduce ambiguities.
Note too that all other "literals" also cannot be used in that position:
4[1]; "hello"[1]; true[1]; nil[1]
But, in the end, it all boils down to taste.
-- Roberto