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Bug 1730

Summary:	Inconsistent behaviour when multiplying CWiseUnaryViews
Product:	Eigen	Reporter:	Andrew Johnson <andrew.r.johnson>
Component:	Core - matrix products	Assignee:	Nobody <eigen.nobody>
Status:	NEW ---
Severity:	Compilation Problem	CC:	andrew.r.johnson, chtz, gael.guennebaud
Priority:	Normal
Version:	3.3 (current stable)
Hardware:	All
OS:	All
Whiteboard:

Description Andrew Johnson 2019-07-11 06:36:18 UTC

Initially discussed on SO [here](https://stackoverflow.com/questions/56635122/using-coeffref-with-const-cwiseunaryview-failing-when-multiplying-two-cwiseuna)

Compilation errors occur when attempting to multiplying two CWiseUnaryViews together, but only under particular constructions.

Given a view that simply returns the same matrix, the compilation fails with an error about ```coefReff``` : [https://godbolt.org/z/JYQb3d](https://godbolt.org/z/JYQb3d)

Given a view that returns the double from a struct nested in another struct, the compilation fails unless the intermediary struct also contains a double: [https://godbolt.org/z/7nvhqx](https://godbolt.org/z/7nvhqx)

However, this intermediary double isn't required if the nested value to be returned is a float: [https://godbolt.org/z/GJUZ41](https://godbolt.org/z/GJUZ41)

Comment 1 Andrew Johnson 2019-07-11 06:39:49 UTC

The formatting for the links hasn't gone well, here they are again:

Given a view that simply returns the same matrix, the compilation fails with an error about ```coefReff``` : https://godbolt.org/z/JYQb3d

Given a view that returns the double from a struct nested in another struct, the compilation fails unless the intermediary struct also contains a double: https://godbolt.org/z/7nvhqx

However, this intermediary double isn't required if the nested value to be returned is a float: https://godbolt.org/z/GJUZ41

Comment 2 Nobody 2019-12-04 18:42:30 UTC

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