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由 Alex Crichton 提交于
This is a continuation of the work done in #13184 to make struct fields private by default. This commit finishes RFC 4 by making all tuple structs have private fields by default. Note that enum variants are not affected. A tuple struct having a private field means that it cannot be matched on in a pattern match (both refutable and irrefutable), and it also cannot have a value specified to be constructed. Similarly to private fields, switching the type of a private field in a tuple struct should be able to be done in a backwards compatible way. The one snag that I ran into which wasn't mentioned in the RFC is that this commit also forbids taking the value of a tuple struct constructor. For example, this code now fails to compile: mod a { pub struct A(int); } let a: fn(int) -> a::A = a::A; //~ ERROR: first field is private Although no fields are bound in this example, it exposes implementation details through the type itself. For this reason, taking the value of a struct constructor with private fields is forbidden (outside the containing module). RFC: 0004-private-fields
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