If I have an

Input

or

Output

that may be

undefined

, because it's an optional parameter, is it better to represent that as

foo?: Output<string>

, or

foo: Output<string | undefined>

in my class (and the same for

Input

in my

args

interface)? Mainly I'm thinking for stuff like

pulumi.all

, does it handle a given value being

undefined

, or does it expect all values to be something that can be resolved to a concrete value at run-time, even if that concrete value is

undefined

? I can test this pretty easily and see if it works, but I was also wondering what would be recommended as best practise in Pulumi.

As a user of a component resource or similar, I'd prefer if outputs were always be there, so

Output<string | undefined>

is my preference. For inputs on my own component resources, I find that I rarely need to support optional parameters where the "optionality" is an output: that is, I know at code-writing time whether or not the value is getting passed in. So generally I provide those as optional

Input<string>

parameters. However if you want to allow an

Output<string | undefined>

to be a parameter, then obviously you have no choice. I see both in Pulumi-provided code, but

Input<string | undefined>

does seem to be more common.