Paul Evans

NAME

Syntax::Keyword::Dynamically - dynamically change the value of a variable

SYNOPSIS

   use Syntax::Keyword::Dynamically;

   my $logger = ...;

   sub operate
   {
      dynamically $logger->level = LOG_DEBUG;

      do_things();
   }

DESCRIPTION

This module provides a syntax plugin that implements a single keyword, dynamically, which alters the behaviour of a scalar assignment operation. Syntactically and semantically it is similar to the built-in perl keyword local, but is implemented somewhat differently to give two key advantages over regular local:

  • You can dynamically assign to lvalue functions and accessors.

  • You can dynamically assign to regular lexical variables.

Semantically, the behaviour can be considered equivalent to

   {
      my $old = $VAR;
      $VAR = "new value";

      ...

      $VAR = $old;
   }

Except that the old value will also be restored in the case of exceptions, goto, next/last/redo or similar ways to leave the controlling block scope.

KEYWORDS

dynamically

   {
      dynamically LVALUE = EXPR;
      ...
   }

The dynamically keyword modifies the behaviour of the following expression. which must be a scalar assignemnt. Before the new value is assigned to the lvalue, its current value is captured and stored internally within the Perl interpreter. When execution leaves the controlling block for whatever reason, as part of block scope cleanup the saved value is restored.

The LVALUE may be any kind of expression that allows normal scalar assignment; lexical or package scalar variables, elements of arrays or hashes, or the result of calling an :value function or method.

If the LVALUE has any GET magic associated with it (including a FETCH method of a tied scalar) then this will be executed exactly once when the dynamically expression is evaluated.

If the LVALUE has any SET magic associated with it (including a STORE method of a tied scalar) then this will be executed exactly once when the dynamically expression is evaluated, and again a second time when the controlling scope is unwound.

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>