in reply to Re^2: my (0?$a:$b): a koan
in thread my (0?$a:$b): a koan

it is surprising that it parses at all, since I thought "my" took a list of variables

I suspect that it takes any expression, then checks if the expression is valid. 

>perl -e"my ( f($x, $y.) );"
syntax error at -e line 1, near ".) "
Execution of -e aborted due to compilation errors.

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The catch here is that that constant folding happens before the check.

Another allowed expression: 

>perl -e"my(my(my(my $sharona)))"

>

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Re^4: my (0?$a:$b): a koan
by JavaFan (Canon) on May 05, 2011 at 16:58 UTC
    I suspect that it takes any expression, then checks if the expression is valid.
    Yeah, but even then, it will reject most expressions: 
    $perl -we 'my(f($x))'
Can't declare subroutine entry in "my" at -e line 1, at EOF
Execution of -e aborted due to compilation errors.

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    Now, my does return an lvalue, and ?: can, but that isn't enough in itself for it to be accepted by my: 
    $ perl -we 'my($x = 3)'
Can't declare scalar assignment in "my" at -e line 1, at EOF
Execution of -e aborted due to compilation errors.

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    What the reason is that my(my $x) and my(0?$x:$y) are accept isn't clear to me.

    This one is interesting: 

    $ perl -we 'my(local $x)'
Can't localize lexical variable $x at -e line 1.
$ perl -we 'perl -we 'local(my $x)'
Can't localize lexical variable $x at -e line 1.
$

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    Regardless of the nesting of local and my, we get the same error message.

    Mixing state and my: 

    $ perl -wE 'sub f {state (my $x); say ++$x} f; f;'
1
1
$ perl -wE 'sub f {my (state $x); say ++$x} f; f;'
1
2
$ perl -wE 'sub f {state my $x; say ++$x} f; f;'
No such class my at -e line 1, near "{state my"
Execution of -e aborted due to compilation errors.

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    Mixing our and local: 
    $ perl -wE 'sub f {our local $x; say ++$x} f; f;'
No such class local at -e line 1, near "{our local"
Execution of -e aborted due to compilation errors.
$ perl -wE 'sub f {our (local $x); say ++$x} f; f;'
1
1
$ perl -wE 'sub f {local our $x; say ++$x} f; f;'
1
1
$

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    So we can have our (local $x), local our $x, but our local $x doesn't parse.
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      What the reason is that my(my $x) and my(0?$x:$y) are accept isn't clear to me.

      my(0?$x:$y) gets constant-folded to valid my($y). The validity checker apparently runs after constant-folding.

      $lex and my $lex are the same op. The only difference is the LVINTRO flag. The validity checker apparently doesn't check the flag.

      Can't localize lexical variable $x

      This is consistent with my guess at the workings, that any variable lookup in the my argument expression is taken to be a lexical declaration. local craps out on the lexical passed to it. (Don't forget, local doesn't declare variables.)

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        Constant-folding can confuse the interpreter? Impossible!

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