Strange Perl line : Return the result of a function to a function

[AlexHWGUY]

I never done a Perl code before but I done some C, PHP, JAVA, etc...
Peel looked very similar before I failed to understand those lines :

substr($y, 5, 2) = substr($y, 4, 2);
substr($y, 4, 1) = ".";

How that possible ? It is replacing the 2 char at pos 5 with 2 char at
pos 4 ?

Thanks to help me put my eyes back in their hole.

 

[Josef Moellers]

I never done a Perl code before but I done some C, PHP, JAVA, etc...
Peel looked very similar before I failed to understand those lines :

substr($y, 5, 2) = substr($y, 4, 2);
substr($y, 4, 1) = ".";

How that possible ? It is replacing the 2 char at pos 5 with 2 char at
pos 4 ?

Thanks to help me put my eyes back in their hole.

It does indeed look strange, but (from "perldoc -f substr"):

"You can use the substr() function as an lvalue, in which case EXPR must
itself be an lvalue."

So it works as designed.

 

[Tad McClellan]

It does indeed look strange, but (from "perldoc -f substr"):

"You can use the substr() function as an lvalue, in which case EXPR must
itself be an lvalue."

So it works as designed.

And if you use the 4-argument form of substr(), then your eyeballs will
stay in their sockets.

 

[Peter J. Holzer]

I never done a Perl code before but I done some C, PHP, JAVA, etc...
Peel looked very similar before I failed to understand those lines :

substr($y, 5, 2) = substr($y, 4, 2);
substr($y, 4, 1) = ".";

How that possible ? It is replacing the 2 char at pos 5 with 2 char at
pos 4 ?

Yes.

That form is now by many considered deprecated, but I wonder whether the
alternative

substr($y, 5, 2, substr($y, 4, 2));
substr($y, 4, 1, ".");

is really more readable. At least the assignment makes it clear what is
replaced (you obviously found the right answer without checking the
manual), while for the 4-argument form you have to look up the manual to
find out that there is a replacement at all.

hp

PS: For replacing parts of a string I prefer the s/// operator, even if
it is somewhat slower.

 

[Ingo Menger]

Yes.

That form is now by many considered deprecated, but I wonder whether the
alternative

substr($y, 5, 2, substr($y, 4, 2));
substr($y, 4, 1, ".");

is really more readable.

Full ACK. After all, people are used to read and write things like

$a[2] = 42;

without ever noticing that the construct on the left hand side means
something totally different when it is used on the right hand side.

 

[John W. Krahn]

I never done a Perl code before but I done some C, PHP, JAVA, etc...
Peel looked very similar before I failed to understand those lines :

substr($y, 5, 2) = substr($y, 4, 2);
substr($y, 4, 1) = ".";

How that possible ? It is replacing the 2 char at pos 5 with 2 char at
pos 4 ?

Yes.

That could also be written as:

substr $y, 4, 3, '.' . substr $y, 4, 2;


John