Provided by: libmojolicious-perl_9.33+dfsg-1_all bug

NAME

       Mojo::Promise - Promises/A+

SYNOPSIS

         use Mojo::Promise;
         use Mojo::UserAgent;

         # Wrap continuation-passing style APIs with promises
         my $ua = Mojo::UserAgent->new;
         sub get_p {
           my $promise = Mojo::Promise->new;
           $ua->get(@_ => sub ($ua, $tx) {
             my $err = $tx->error;
             if   (!$err || $err->{code}) { $promise->resolve($tx) }
             else                         { $promise->reject($err->{message}) }
           });
           return $promise;
         }

         # Perform non-blocking operations sequentially
         get_p('https://mojolicious.org')->then(sub ($mojo) {
           say $mojo->res->code;
           return get_p('https://metacpan.org');
         })->then(sub ($cpan) {
           say $cpan->res->code;
         })->catch(sub ($err) {
           warn "Something went wrong: $err";
         })->wait;

         # Synchronize non-blocking operations (all)
         my $mojo = get_p('https://mojolicious.org');
         my $cpan = get_p('https://metacpan.org');
         Mojo::Promise->all($mojo, $cpan)->then(sub ($mojo, $cpan) {
           say $mojo->[0]->res->code;
           say $cpan->[0]->res->code;
         })->catch(sub ($err) {
           warn "Something went wrong: $err";
         })->wait;

         # Synchronize non-blocking operations (race)
         my $mojo = get_p('https://mojolicious.org');
         my $cpan = get_p('https://metacpan.org');
         Mojo::Promise->race($mojo, $cpan)->then(sub ($tx) {
           say $tx->req->url, ' won!';
         })->catch(sub ($err) {
           warn "Something went wrong: $err";
         })->wait;

DESCRIPTION

       Mojo::Promise is a Perl-ish implementation of Promises/A+ <https://promisesaplus.com> and
       a superset of ES6 Promises <https://duckduckgo.com/?q=n%20Promise>.

STATES

       A promise is an object representing the eventual completion or failure of a non-blocking
       operation. It allows non-blocking functions to return values, like blocking functions. But
       instead of immediately returning the final value, the non-blocking function returns a
       promise to supply the value at some point in the future.

       A promise can be in one of three states:

       pending
         Initial state, neither fulfilled nor rejected.

       fulfilled
         Meaning that the operation completed successfully.

       rejected
         Meaning that the operation failed.

       A pending promise can either be fulfilled with a value or rejected with a reason. When
       either happens, the associated handlers queued up by a promise's "then" method are called.

ATTRIBUTES

       Mojo::Promise implements the following attributes.

   ioloop
         my $loop = $promise->ioloop;
         $promise = $promise->ioloop(Mojo::IOLoop->new);

       Event loop object to control, defaults to the global Mojo::IOLoop singleton. Note that
       this attribute is weakened.

METHODS

       Mojo::Promise inherits all methods from Mojo::Base and implements the following new ones.

   all
         my $new = Mojo::Promise->all(@promises);

       Returns a new Mojo::Promise object that either fulfills when all of the passed
       Mojo::Promise objects have fulfilled or rejects as soon as one of them rejects. If the
       returned promise fulfills, it is fulfilled with the values from the fulfilled promises in
       the same order as the passed promises.

   all_settled
         my $new = Mojo::Promise->all_settled(@promises);

       Returns a new Mojo::Promise object that fulfills when all of the passed Mojo::Promise
       objects have fulfilled or rejected, with hash references that describe the outcome of each
       promise.

   any
         my $new = Mojo::Promise->any(@promises);

       Returns a new Mojo::Promise object that fulfills as soon as one of the passed
       Mojo::Promise objects fulfills, with the value from that promise.

   catch
         my $new = $promise->catch(sub {...});

       Appends a rejection handler callback to the promise, and returns a new Mojo::Promise
       object resolving to the return value of the callback if it is called, or to its original
       fulfillment value if the promise is instead fulfilled.

         # Longer version
         my $new = $promise->then(undef, sub {...});

         # Pass along the rejection reason
         $promise->catch(sub (@reason) {
           warn "Something went wrong: $reason[0]";
           return @reason;
         });

         # Change the rejection reason
         $promise->catch(sub (@reason) { "This is bad: $reason[0]" });

   clone
         my $new = $promise->clone;

       Return a new Mojo::Promise object cloned from this promise that is still pending.

   finally
         my $new = $promise->finally(sub {...});

       Appends a fulfillment and rejection handler to the promise, and returns a new
       Mojo::Promise object resolving to the original fulfillment value or rejection reason.

         # Do something on fulfillment and rejection
         $promise->finally(sub { say "We are done!" });

   map
         my $new = Mojo::Promise->map(sub {...}, @items);
         my $new = Mojo::Promise->map({concurrency => 3}, sub {...}, @items);

       Apply a function that returns a Mojo::Promise to each item in a list of items while
       optionally limiting concurrency.  Returns a Mojo::Promise that collects the results in the
       same manner as "all". If any item's promise is rejected, any remaining items which have
       not yet been mapped will not be.

         # Perform 3 requests at a time concurrently
         Mojo::Promise->map({concurrency => 3}, sub { $ua->get_p($_) }, @urls)
           ->then(sub{ say $_->[0]->res->dom->at('title')->text for @_ });

       These options are currently available:

       concurrency
           concurrency => 3

         The maximum number of items that are in progress at the same time.

   new
         my $promise = Mojo::Promise->new;
         my $promise = Mojo::Promise->new(sub {...});

       Construct a new Mojo::Promise object.

         # Wrap a continuation-passing style API
         my $promise = Mojo::Promise->new(sub ($resolve, $reject) {
           Mojo::IOLoop->timer(5 => sub {
             if (int rand 2) { $resolve->('Lucky!') }
             else            { $reject->('Unlucky!') }
           });
         });

   race
         my $new = Mojo::Promise->race(@promises);

       Returns a new Mojo::Promise object that fulfills or rejects as soon as one of the passed
       Mojo::Promise objects fulfills or rejects, with the value or reason from that promise.

   reject
         my $new  = Mojo::Promise->reject(@reason);
         $promise = $promise->reject(@reason);

       Build rejected Mojo::Promise object or reject the promise with one or more rejection
       reasons.

         # Longer version
         my $promise = Mojo::Promise->new->reject(@reason);

   resolve
         my $new  = Mojo::Promise->resolve(@value);
         $promise = $promise->resolve(@value);

       Build resolved Mojo::Promise object or resolve the promise with one or more fulfillment
       values.

         # Longer version
         my $promise = Mojo::Promise->new->resolve(@value);

   then
         my $new = $promise->then(sub {...});
         my $new = $promise->then(sub {...}, sub {...});
         my $new = $promise->then(undef, sub {...});

       Appends fulfillment and rejection handlers to the promise, and returns a new Mojo::Promise
       object resolving to the return value of the called handler.

         # Pass along the fulfillment value or rejection reason
         $promise->then(
           sub (@value) {
             say "The result is $value[0]";
             return @value;
           },
           sub (@reason) {
             warn "Something went wrong: $reason[0]";
             return @reason;
           }
         );

         # Change the fulfillment value or rejection reason
         $promise->then(
           sub (@value)  { return "This is good: $value[0]" },
           sub (@reason) { return "This is bad: $reason[0]" }
         );

   timer
         my $new  = Mojo::Promise->timer(5 => 'Success!');
         $promise = $promise->timer(5 => 'Success!');
         $promise = $promise->timer(5);

       Create a new Mojo::Promise object with a timer or attach a timer to an existing promise.
       The promise will be resolved after the given amount of time in seconds with or without a
       value.

   timeout
         my $new  = Mojo::Promise->timeout(5 => 'Timeout!');
         $promise = $promise->timeout(5 => 'Timeout!');
         $promise = $promise->timeout(5);

       Create a new Mojo::Promise object with a timeout or attach a timeout to an existing
       promise. The promise will be rejected after the given amount of time in seconds with a
       reason, which defaults to "Promise timeout".

   wait
         $promise->wait;

       Start "ioloop" and stop it again once the promise has been fulfilled or rejected, does
       nothing when "ioloop" is already running.

DEBUGGING

       You can set the "MOJO_PROMISE_DEBUG" environment variable to get some advanced diagnostics
       information printed to "STDERR".

         MOJO_PROMISE_DEBUG=1

SEE ALSO

       Mojolicious, Mojolicious::Guides, <https://mojolicious.org>.