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Why does ParseBoolError have the _priv field:
pub struct ParseBoolError {
_priv: (),
}
I don't think that the _priv field is used.
524
Struct members, including nested classes and structs, can be declared public , internal , or private . Class members, including nested classes and structs, can be public , protected internal , protected , internal , private protected , or private .
In a normal scenario, the visibility of the struct in Rust is private and it can be made public by making use of the pub modifier. It should be noted that this case of visibility only makes sense when we are trying to access the struct fields from outside the module, from where it is defined.
You can't create an instance of a struct if it has private fields. This is just a trick to prevent ParseBoolError from being constructed in user code.
One reason to do this is for forwards compatibility. If users could create it with:
let error = ParseBoolError {};
then a future version of ParseBoolError couldn't add fields without breaking that code.
76
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