https://github.com/robrwo/perlx-let

Syntactic sugar for lexical constants
https://github.com/robrwo/perlx-let

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Syntactic sugar for lexical constants

• Host: GitHub
• URL: https://github.com/robrwo/perlx-let
• Owner: robrwo
• Created: 2019-02-08T17:09:25.000Z (almost 6 years ago)
• Default Branch: master
• Last Pushed: 2023-06-14T20:35:01.000Z (over 1 year ago)
• Last Synced: 2023-08-20T22:06:31.657Z (about 1 year ago)
• Language: Perl
• Size: 47.9 KB
• Stars: 2
• Watchers: 2
• Forks: 0
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • Changelog: Changes

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README

        
# NAME

PerlX::Let - Syntactic sugar for lexical state constants

# VERSION

version v0.3.0

# SYNOPSIS

```perl

use PerlX::Let;

{

    let $x = 1;

    let $y = "string";

    if ( ($a->($y} - $x) > ($b->{$y} + $x) )

    {

      something( $y, $x );

    }

}

```

# DESCRIPTION

This module allows you to define lexical constants using a new `let`

keyword, for example, code such as

```perl

if (defined $arg{username}) {

  $row->update( { username => $arg{username} );

}

```

is liable to typos. You could simplify it with

```perl

{

    let $key = "username";

    if (defined $arg{$key}) {

        $row->update( { $key => $arg{$key} );

    }

}

```

This is roughly equivalent to using

```perl

use Const::Fast ();

{

    use feature 'state';

    state $key = "username";

    unless (state $_flag = 0) {

        Const::Fast::_make_readonly( \$key );

        $_flag = 1;

    }

    if (defined $arg{$key}) {

        $row->update( { $key => $arg{$key} );

    }

}

```

However, if the value contains a sigil, or (for versions of Perl

before 5.28) the value is not a scalar, then this uses a my variable

```perl

use Const::Fast ();

{

    Const::Fast::const my $key => "username";

    if (defined $arg{$key}) {

        $row->update( { $key => $arg{$key} );

    }

}

```

The reason for using state variables is that it takes time to mark a

variable as read-only, particularly for deeper data structures.

However, the tradeoff for using this is that the variables remain

allocated until the process exits.

# KNOWN ISSUES

A let assignment will enable the state feature inside of the current

context.

The parsing of assignments is rudimentary, and may fail when assigning

to another variable or the result of a function.  Because of this,

you may get unusual error messages for syntax errors, e.g.

"Transliteration pattern not terminated".

Because this modifies the source code during compilation, the line

numbers may be changed, particularly if the let assignment(s) are on

multiple lines.

# SUPPORT FOR OLDER PERL VERSIONS

The this module requires Perl v5.12 or later.

Future releases may only support Perl versions released in the last ten years.

# SEE ALSO

[feature](https://metacpan.org/pod/feature)

[Const::Fast](https://metacpan.org/pod/Const%3A%3AFast)

[Keyword::Simple](https://metacpan.org/pod/Keyword%3A%3ASimple)

# AUTHOR

Robert Rothenberg 

# COPYRIGHT AND LICENSE

This software is Copyright (c) 2019-2023 by Robert Rothenberg.

This is free software, licensed under:

```

The Artistic License 2.0 (GPL Compatible)

```