t.i.t.deferLater() callable argument should be optional

[twisted-trac]

	@twm reported
Trac ID	trac#9577
Type	enhancement
Created	2019-01-20 01:41:03Z
Branch	https://github.com/twisted/twisted/tree/9577-deferLater-no-callback

Right now this is the idiomatic way to generate a Deferred that fires after ten seconds:

from twisted.internet.task import deferLater

d = deferLater(reactor, 10.0, lambda: None)

Instead, we should be able to write:

d = deferLater(reactor, 10.0)

In this case d would fire with None.

The increase in convenience is modest, but non-negligible. In practice every Twisted codebase I adopt has an equivalent function, usually named sleep or asleep. Usually this helper has one of two flaws:

1. It doesn't implement cancellation (while deferLater does).
2. It is a wrapper around deferLater, incurring the unnecessary overhead of allocating and calling the callback required by that function.

There is some historical debate about this in #1875.

Searchable metadata

trac-id__9577 9577
type__enhancement enhancement
reporter__twm twm
priority__normal normal
milestone__None None
branch__9577_deferLater_no_callback 9577-deferLater-no-callback
branch_author__ 
status__closed closed
resolution__fixed fixed
component__core core
keywords__None None
time__1547948463530949 1547948463530949
changetime__1554786206341084 1554786206341084
version__None None
owner__twm twm

[twisted-trac]

	@twm set owner to @twm @twm set status to assigned

[twisted-trac]

	@twm removed owner @twm set status to new

PR ready for review: #1094

[twisted-trac]

	@glyph set owner to @twm

#1094 (review)

[twisted-trac]

	@twm set status to closed

In changeset ee9c5db

#!CommitTicketReference repository="" revision="ee9c5db3b94e1475eec31314bcac93f71501e7a1"
Merge pull request #1094 from twisted/9577-deferLater-no-callback

Author: twm
Reviewer: glyph
Fixes: ticket:9577

Make callback argument to deferLater optional