RFC: Remove the priv keyword

active/0000-remove-priv.md

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+- Start Date: 2014-03-31
+- RFC PR #: (leave this empty)
+- Rust Issue #: (leave this empty)
+
+# Summary
+
+This RFC is a proposal to remove the usage of the keyword `priv` from the Rust
+language.
+
+# Motivation
+
+By removing `priv` entirely from the language, it significantly simplifies the
+privacy semantics as well as the ability to explain it to newcomers. The one
+remaining case, private enum variants, can be rewritten as such:
+
+```rust
+// pub enum Foo {
+//     Bar,
+//     priv Baz,
+// }
+
+pub enum Foo {
+    Bar,
+    Baz(BazInner)
+}
+
+pub struct BazInner(());
+
+// pub enum Foo2 {
+//     priv Bar2,
+//     priv Baz2,
+// }
+
+pub struct Foo2 {
+    variant: FooVariant
+}
+
+enum FooVariant {
+    Bar2,
+    Baz2,
+}
+```
+
+Private enum variants are a rarely used feature of the language, and are
+generally not regarded as a strong enough feature to justify the `priv` keyword
+entirely.
+
+# Detailed design
+
+There remains only one use case of the `priv` visibility qualifier in the Rust
+language, which is to make enum variants private. For example, it is possible
+today to write a type such as:
+
+```rust
+pub enum Foo {
+    Bar,
+    priv Baz
+}
+```
+
+In this example, the variant `Bar` is public, while the variant `Baz` is
+private. This RFC would remove this ability to have private enum variants.
+
+In addition to disallowing the `priv` keyword on enum variants, this RFC would
+also forbid visibility qualifiers in front of enum variants entirely, as they no
+longer serve any purpose.
+
+### Status of the identifier `priv`
+
+This RFC would demote the identifier `priv` from being a keyword to being a
+reserved keyword (in case we find a use for it in the future).
+
+# Alternatives
+
+* Allow private enum variants, as-is today.
+* Add a new keyword for `enum` which means "my variants are all private" with
+  controls to make variants public.
+
+# Unresolved questions
+
+* Is the assertion that private enum variants are rarely used true? Are there
+  legitimate use cases for keeping the `priv` keyword?