Ian Downes created MESOS-785:
--------------------------------
Summary: Extend stout/try to support functional composition
Key: MESOS-785
URL: https://issues.apache.org/jira/browse/MESOS-785
Project: Mesos
Issue Type: Improvement
Reporter: Ian Downes
Priority: Minor
Motivating example was fetching a list of URIs where each 'fetch' is actually a
sequence of operations: fetch the uri to a local file, pass the local file on
to chmod or extract, and pass on to chown it or the directory. Individual
operations needn't be asynchronous.
This can be written using Futures but is potentially confusing when the code is
actually synchronous.
Future<Nothing> fetch(
const CommandInfo& commandInfo,
const string& directory,
const HDFS& hdfs,
const Option<string>& frameworks_home,
const Option<string>& user)
{
foreach (const CommandInfo::URI& uri, commandInfo.uris()) {
bool executable = uri.has_executable() && uri.executable();
// This code is synchronous!
Future<string> result =
_fetch(uri, directory, hdfs, frameworks_home)
.then(lambda::bind(_chmod, lambda::_1, directory, executable))
.then(lambda::bind(_extract, lambda::_1, directory, !executable))
.then(lambda::bind(_chown, lambda::_1, directory, user));
if (result.isFailed()) {
LOG(ERROR) << "Fetch of uri '" << uri.value() << "' failed: " <<
result.failure();
return Future<Nothing>::failed(result.failure());
}
}
return Nothing();
}
[~bmahler] and I had these thoughts:
* .ifSome() and .ifError() to express control flow.
* .and() for chaining to make it clear the code is synchronous and also that it
will short-circuit error.
e.g.
Try<string> result =
_fetch(...)
.and(chmod...)
.and(extract...)
.and(chown...);
Thoughts? How do other languages express this?
--
This message was sent by Atlassian JIRA
(v6.1#6144)
