Add @examplesIf tag

[gaborcsardi]

Quite simple. Let me know what you think.

Closes #962.

[hadley]

Has anything else changed that requires us to rethink this, or should I review it as is?

[gaborcsardi]

@hadley Good as it is, well, except that it needs NEWS and docs, if we decide to go with this. FWIW I use it in several packages and seems to work well.

[krlmlr]

If every line of code has its own if() block -- do we still need withAutoprint() and braces?

foo <- TRUE
if (foo) "foo"
#> [1] "foo"
if (foo) if (TRUE) "bar" else "baz"
#> [1] "bar"
if (foo) if (FALSE) "bar" else "baz"
#> [1] "baz"

^{Created on 2020-06-08 by the reprex package (v0.3.0)}

[gaborcsardi]

@krlmlr hmmm, it is no obvious to me that you can do that. E.g. how about multi-line strings? Or raw strings? You could parse the expression, but this is starting to get much more complicated than withAutoprint(). I am not even sure what is wrong with withAutoprint()?

[krlmlr]

Got you. I thought this pattern is applied to every statement. In this case withAutoprint() is just fine. I'll test-drive in my packages.

[gaborcsardi]

@krlmlr Thanks!

[hadley]

Can you add a news bullet? I'd like to merge this just so we can experiment a bit more with it (without advertising it heavily)

[gaborcsardi]

(Closed by mistake.)

@hadley So, this version does not handle examples in R6 classes, which are special. It would need this commit to handle them: gaborcsardi/roxygenlabs@fc249f5

Should I add that?

[hadley]

I think we should leave R6 for now

[gaborcsardi]

@hadley Added NEWS bullet.