On Tue, Jul 24, 2001 at 02:32:18PM -0300, Silvio Luis Leite Santana wrote:
> #!/usr/bin/perl -w
> use strict;
>
> our $PI;
>
> $PI = \3.1415926535;
> print "(1) $PI\n";
> # prints SCALAR(0x8101f64)
>
> $PI = 7;
> print "(2) $PI\n";
> # prints 7
>
> *PI = \4.31415926;
> print "(3) $PI\n";
> # prints 4.31415926
>
> $PI = \5.31419526;
> # error: Modification of a read-only value attempted at ./m2 line 18.
> print "(4) $PI\n";
>
> And now the questions:
>
> Question 1) Ignoring the different constant values,
> Is the first and the third attributions equivalent?
I'm not sure how you're using "attribution" here. Do you mean assignment?
No, the first ($PI = \3.1415926535) and third (*PI = \4.31415926)
assignments are not equivalent, as evidenced by the value you get back when
you print it. The first assignment is assigning a scalar reference to $PI,
the third is filling the scalar slot of the PI glob with the value
4.31415926.
> It seems that not, but then, why?
> I thought that when I wrote
> *PI = \value
> I was giving the scalar $PI the value "reference to a value",
> and not the value itself (that is what's being printed)!?
You aren't, you are filling the scalar slot of the PI glob with a value. If
that value is a constant then $PI is read-only, because you can't change a
constant.
> Question 2) Why cannot we make the 4th attribution? What is
> making the scalar $PI a read-only?
The third assignment makes it read-only.
> It cannot be the previous reference, because we also set it to a reference
> on the first attribution, but we could change it on the second...
It can be on the previous reference because "$PI = \3.1415926535" is very
different from "*PI = \4.31415926".
Michael
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