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The very useful TryFrom trait landed only in 1.34, so hopefully the code using unwrap_or_else() in From impl predates that...

Actually the From trait documentation is now extremely clear about when to implement it (https://doc.rust-lang.org/std/convert/trait.From.html#when-t...)

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As someone unfamiliar with Rust (yet! it's on my ever growing list of things I'd like to absorb into my brain), unwrap_or_else() sounds like part of the "What You See Is What I Threatened the Computer To Do" paradigm.

> INTERCAL has many other features designed to make it even more aesthetically unpleasing to the programmer: it uses statements such as "READ OUT", "IGNORE", "FORGET", and modifiers such as "PLEASE". This last keyword provides two reasons for the program's rejection by the compiler: if "PLEASE" does not appear often enough, the program is considered insufficiently polite, and the error message says this; if it appears too often, the program could be rejected as excessively polite.

Oh wow! That's amazing! "I came to learn Computer Science, but I left with good bedside manners".

Immediately thought of INTERCAL :)

There are also the equally threatening and useful `map_or_else` (on Result and Option) and `ok_or_else` (on Option and experimentally on bool)

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