x.copy(a=b)

usually return an instance of the same type of

x

. Here it wouldn't be possible and wouldn't make sense as thread dispatcher never contains

Job

element. with

+

you explicitly build a new object (A context) which contains "the dispatcher + the job"

The problem with

+

for forming contexts is that it is not explicit what part of context is changing. For example

context + job

replaces the current parent with

job

, but it is implicit. The

launch(context, parent = job)

is an attempt to fix that issue. In a sense,

context.copy(parent = job)

is

+

with explicit naming

The advantage of having

context.copy(...)

is that it is defined once for all context, not in every builder like

launch

. Plus it can be generalized to include other parameters like

context.copy(name = ":)")

And

+

is already "defined once for all context". As you said, there is conceptually no difference between the

+

and the

copy

you propose. Except that a good

x.copy()

function (IMO) should always return an instance of the same type than

x

(like it is the case for data classes). And this is is not possible with a

CoroutineDispatcher

. Because instances of `CoroutineDispatcher`would never contains any parent

Job

.