[swift-dev] Optionals in swift-clang

Seth Friedman sethfri at gmail.com
Tue Dec 8 19:59:57 CST 2015

Hi all,

In Optional.swift in the stdlib, there's a comment that says "The compiler
has special knowledge of Optional<Wrapped>, including the fact that it is
an enum with cases named 'None' and 'Some'."

What I'm trying to understand is: If I wanted to implement the optional
type from scratch, what would be the process I would go through? I've
scoured the swift-clang project and can't seem to find any reference to
optionals or even Swift explicitly. I discovered nullability attributes and
am hypothesizing that an expression of something like "Type?" is somehow
mapped to an attribute, but I'm really just stumbling around in the dark.

In terms of what I've tried, I've gone through a lot of the source in the
swift-clang lib/Basic and lib/AST directories, and I've read through the
"Clang CFE Internals Manual" on the Clang website.

Help is much appreciated!

Thanks in advance,
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