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fetch 

        # Thread.fetch

(from ruby core)
---
    thr.fetch(sym)           -> obj
    thr.fetch(sym) { }       -> obj
    thr.fetch(sym, default)  -> obj

---

Returns a fiber-local for the given key. If the key can't be found,
there are several options: With no other arguments, it will raise a
KeyError exception; if *default* is given, then that will be returned;
if the optional code block is specified, then that will be run and its
result returned.  See Thread#[] and Hash#fetch.

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