[Templates] Assign and print at the same time

[Paul Seamons]

On Monday 17 September 2007, Brad Bowman wrote:
> Is there a way to assign and display a calculation in one statement?
>
>    [% SGET a = 1 + 2 # set "a" to 3 and display it %]
>
> Currently I'm doing [% a = ...; a %] which is fine...
>
> Brad

Yes.

perl -e 'use Template; Template->new->process(
  \"[% (a = 1 + 2) %] = [% a %]\n"
)'
3 = 3

The parens are the trick.  It changes the operation from a set operation to a 
GET that evaluates its statement.  This is actually similar in scope to why 
[% WHILE (f = f + 1) %] needs the parens.

On a further note:

This also works in Template::Alloy.  Interestingly Template::Alloy also 
requires the parents on self modifiers if you want the result to display:

use Template::Alloy; Template::Alloy->new->process(\"[% a+=1 %] = [% a %]\n")'
 = 1

perl -e 'use Template::Alloy; Template::Alloy->new->process(\"[% (a+=1) %] = 
[% a %]\n")'
1 = 1

Though Andy hasn't specified this for TT3, I think that the Template::Alloy 
behavior is consistent with the current behavior of Template and is how TT3 
ought to behave.

However pre and post increment should print their result immediately - which 
is what Template::Alloy does.

perl -e 'use Template::Alloy; Template::Alloy->new->process(\"[% a++ %] = [% 
a %]\n")'
0 = 1

perl -e 'use Template::Alloy; Template::Alloy->new->process(\"[% ++a %] = [% 
a %]\n")'
1 = 1

Paul Seamons