Issue #10783 has been reported by Antonio Scandurra.

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Misc #10783: String#concat has an "appending" behavior
https://bugs.ruby-lang.org/issues/10783

* Author: Antonio Scandurra
* Status: Open
* Priority: Normal
* Assignee: 
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Ruby String documentation (http://www.ruby-doc.org/core-2.2.0/String.html) introduces the two terms **Appending** and **Concatenation**:

- Concatenation (aka `+`) ¡½Returns a new String containing other_str concatenated to str.
- Append (aka `<<`) ¡½Concatenates the given object to str. 

However, calling `concat` results in an appending operation. I find this particularly confusing and against the Principle of Least Surprise (e.g. I'd expect `concat` to actually concatenate something). On the other hand I understand that changing such a small method would result in a quite significant breaking change.

Do you see this as an inconsistency? If yes, is there any particular design(or historical) reason behind it?

Thank you.

P.s. Seems like this is the case for `Array` as well.



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