Use Union{Some{T}, Nothing}

[adkabo]

Currently rewriters don't distinguish between failing to match and successfully returning a value of nothing.

I want to use this pattern:

y = r1(expr)::Union{Nothing, Some{Expr})
return isnothing(y) ? y : nothing : r2(something(y))

Rewriters could be Some-aware and unwrap these values internally with something(x).

References

• A blog post about why this wrapping is good
• A similar issue for Base.get WIP/RFC: add 2-argument get returning Union{Nothing,Some} JuliaLang/julia#34821
• A similar issue for Base.maybetake! add maybetake! and tryput! JuliaLang/julia#41966

[0x0f0f0f]

cc @shashi