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Author image Paul Evans

NAME

Feature::Compat::Try - make try/catch syntax available

SYNOPSIS

   use Feature::Compat::Try;

   sub foo
   {
      try {
         attempt_a_thing();
         return "success";
      }
      catch ($e) {
         warn "It failed - $e";
         return "failure";
      }
   }

DESCRIPTION

This module is written in the aspiration that one day perl will gain true native syntax support for try/catch control flow, and that it will be spelled using the syntax defined here. The intention here is that on such a version of perl that provides this syntax this module will simply enable it, equivalent to perhaps

   use feature 'try';

On older versions of perl before such syntax is available, it is currently provided instead using the Syntax::Keyword::Try module, imported with a special set of options to configure it to recognise exactly and only the same syntax as this as-yet-aspirational core perl feature, thus ensuring that any code using it will still continue to function on that newer perl.

KEYWORDS

try

   try {
      STATEMENTS...
   }
   ...

A try statement provides the main body of code that will be invoked, and must be followed by a catch statement.

Execution of the try statement itself begins from the block given to the statement and continues until either it throws an exception, or completes successfully by reaching the end of the block.

The body of a try {} block may contain a return expression. If executed, such an expression will cause the entire containing function to return with the value provided. This is different from a plain eval {} block, in which circumstance only the eval itself would return, not the entire function.

The body of a try {} block may contain loop control expressions (redo, next, last) which will have their usual effect on any loops that the try {} block is contained by.

The parsing rules for the set of statements (the try block and its associated catch) are such that they are parsed as a self-contained statement. Because of this, there is no need to end with a terminating semicolon.

catch

   ...
   catch ($var) {
      STATEMENTS...
   }

A catch statement provides a block of code to the preceding try statement that will be invoked in the case that the main block of code throws an exception. A new lexical variable is created to store the exception in.

Presence of this catch statement causes any exception thrown by the preceding try block to be non-fatal to the surrounding code. If the catch block wishes to optionally handle some exceptions but not others, it can re-raise it (or another exception) by calling die in the usual manner.

As with try, the body of a catch {} block may also contain a return expression, which as before, has its usual meaning, causing the entire containing function to return with the given value. The body may also contain loop control expressions (redo, next or last) which also have their usual effect.

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>