Improve error message for push_back when using an immutable type
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Possible (wrong) meaning that can be inferred from the current one: this is a subset collection and you are trying to push a mutable object so "Can only add immutable objects to subset collections", therefore you should change your mutable object to immutable object (wrong conclusion).
With the new one I don't think the wrong meaning can be inferred; it means you are pushing an immutable object but "Immutable objects can only be added to subset collections", which means it's not a subset collection, and the answer here is to change from immutable to mutable.
BEGINRELEASENOTES
ENDRELEASENOTES
Possible (wrong) meaning that can be inferred from the current one: this is a subset collection and you are trying to push a mutable object so "Can only add immutable objects to subset collections", therefore you should change your mutable object to immutable object (wrong conclusion).
With the new one I don't think the wrong meaning can be inferred; it means you are pushing an immutable object but "Immutable objects can only be added to subset collections", which means it's not a subset collection, and the answer here is to change from immutable to mutable.