Move CastInPlace behind a feature gate.

Cargo.toml

@@ -19,8 +19,11 @@ extern_crate_std = ["extern_crate_alloc"]
 zeroable_maybe_uninit = []
 zeroable_atomics = []
 min_const_generics = []
-wasm_simd = [] # Until >= 1.54.0 is MSRV this is an off-by-default feature.
-aarch64_simd = [] # Until >= 1.59.0 is MSRV this is an off-by-default feature.
+
+# Off-by-default while bytemuck's MSRV is raised.
+wasm_simd = [] # Requires MSRV >= 1.54.0.
+aarch64_simd = [] # Requires MSRV >= 1.59.0.
+unified_cast = [] # Requires MSRV >= 1.65.0.
 
 # Do not use if you can avoid it, because this is unsound.
 unsound_ptr_pod_impl = []
@@ -42,6 +45,7 @@ features = [
   "zeroable_atomics",
   "min_const_generics",
   "wasm_simd",
+  "unified_cast",
 ]
 
 [package.metadata.playground]
@@ -54,4 +58,5 @@ features = [
   "zeroable_atomics",
   "min_const_generics",
   "wasm_simd",
+  "unified_cast",
 ]

src/lib.rs

@@ -125,7 +125,9 @@ pub use offset_of::*;
 mod transparent;
 pub use transparent::*;
 
+#[cfg(feature = "unified_cast")]
 mod cast;
+#[cfg(feature = "unified_cast")]
 pub use cast::CastInPlace;
 
 #[cfg(feature = "derive")]