List Util insert_at(index, value), delete_at(index)

[ngoc]

Hi
Searching around CPAN to find abstract method for insert and delete
element in a List or Array, but did not find.
Searching for something like insert_at(index, value), delete_at(index)
Thanks
ngoc

 

[John W. Krahn]

Searching around CPAN to find abstract method for insert and delete
element in a List

A list is a literal and cannot be modified at run time.

perldoc -q "What is the difference between a list and an array"

or Array,

perldoc -f splice

but did not find.
Searching for something like insert_at(index, value),

splice @array, $index, 1, 'value';

delete_at(index)

splice @array, $index, 1;



John

 

[Anno Siegel]

Searching around CPAN to find abstract method for insert and delete
element in a List

[...]

but did not find.
Searching for something like insert_at(index, value),

splice @array, $index, 1, 'value';

splice @array, $index, 0, 'value';

Anno

 

[Mintcake]

A list is a literal and cannot be modified at run time.

perldoc -q "What is the difference between a list and an array"

A list is not necessarily a literal.

I looked a the perldoc mentioned and saw the following:

As a side note, there's no such thing as a list in scalar
context.
When you say

$scalar = (2, 5, 7, 9);

you're using the comma operator in scalar context, so it uses the
scalar comma operator. There never was a list there at all!
This
causes the last value to be returned: 9.

Can someone explain what is happening here...

perl -le '$scalar = () = (2, 5, 7, 9); print $scalar'

This prints 4. I've never quite understood why.

 

[Dave]

A list is not necessarily a literal.

I looked a the perldoc mentioned and saw the following:

As a side note, there's no such thing as a list in scalar
context.
When you say

$scalar = (2, 5, 7, 9);

you're using the comma operator in scalar context, so it uses the
scalar comma operator. There never was a list there at all!
This
causes the last value to be returned: 9.

Can someone explain what is happening here...

perl -le '$scalar = () = (2, 5, 7, 9); print $scalar'

This prints 4. I've never quite understood why.

It is equivalent to
perl -le '$scalar = ( () = (2, 5, 7, 9) ); print $scalar'

Camel book p75
'List assignment in scalar context returns the number of elements produced
by the expression on the right side of the assignment'.

 

[Tad McClellan]

John W. Krahn wrote:

you're using the comma operator in scalar context,

Can someone explain what is happening here...

First let me point out that the below has nothing to do with
the comma operator nor with the distinction between a list
and an array.

perl -le '$scalar = () = (2, 5, 7, 9); print $scalar'

This prints 4. I've never quite understood why.

() = (2, 5, 7, 9)

is a "list assignment".

This list assignment is in scalar context because its value
is being assigned to a scalar:

$scalar = <list assignment>

So you store whatever the value of a list assignment in scalar context
is to $scalar.

The value of a list assignment in scalar context is the number
of elements in the right hand side of the list assignment.

This is documented in the "List value constructors" section in perldata.pod.