# Herbert Wolverson - Rust Brain Teasers (Highlights)  ## Highlights - When used with an as keyword, _ indicates that Rust should try to convert the value into whatever type is expected in this context. For example, function_that_requires_a_u32(x as _) will try to convert x—irrespective of its type—to a u32. ([View Highlight](https://read.readwise.io/read/01jycpcp1s1qq2dv1n63q8jehm)) ^905957047 - As it turns out, for loops fall into the unavailable category because they require a Range—prohibited because of the generic bounds restriction. This makes the example code fail to compile. ([View Highlight](https://read.readwise.io/read/01jycqa71epbgfqx4bwqftqc2g)) ^905962043 for is not allowed in a const fn