Type inferrence limitation?

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1

Why does this work:

mail = user.mail # Type is String?

if mail
  env.session.string("user_mail", mail) # Only takes String

And this not?

if user.mail
  env.session.string("user_mail", user.mail)

I would assume they’re the same.

2

https://crystal-lang.org/reference/1.8/syntax_and_semantics/if_var.html#method-calls

tl;dr Procs and methods aren’t guaranteed to return the same more-specific type on two successive calls.

3

Aha… Well, in theory the compiler could notice that user.mail is a simple getter that returns the same insta… Oooh, and the point on why it doesn’t work on instance vars applies…

Makes sense.

4

Yea, otherwise would technically be possible with concurrency to switch to another fiber that mutates the ivar after the initial check that then could cause issues.