As reported by GATE collaboration.
 
Consider the following code:
class MyClass {
G4SPSPosDistribution my_helper;
}

This code will not compile when copy constructor is compiler-generated because G4SPSPosDistribution contains a G4Cache<> data-field that is not-copyable.

While the problem can be addressed at the user-code level (e.g. disabling copy-ctr in user classes), a proper strategy should be implemented to solve the issue in G4 code. 

From a first analysis two strategies seems possible:
A) Transform G4Cache to be copiable
B) Provide a copy-ctr (and ass. operator) of contaier classes (e.g. every class contains a G4Cache<> object) that does not copy the cache and instead initializes a new one.

B) has the drawback of breaking the semantic of the copy-ctr. A) may be more complex to implement.

Andrea