TrustedLen

build.rs

@@ -24,6 +24,10 @@ fn main() {
         println!("cargo:rustc-cfg=feature=\"optimize\"");
     }
 
+    if let Some(true) = version_check::supports_feature("trusted_len") {
+        println!("cargo:rustc-cfg=feature=\"trusted_len\"");
+    }
+
     if env::var("ORJSON_DISABLE_WRITEEXT").is_ok() {
     } else if env::var("ORJSON_ENABLE_WRITEEXT").is_ok()
         || env::var("CARGO_CFG_TARGET_OS").unwrap() == "macos"

src/ffi/dict.rs

@@ -39,4 +39,12 @@ impl Iterator for PyDictIter {
             }
         }
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = ffi!(Py_SIZE(self.dict_ptr)) as usize;
+        (len, Some(len))
+    }
 }
+
+#[cfg(feature = "trusted_len")]
+unsafe impl std::iter::TrustedLen for PyDictIter {}

src/lib.rs

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 #![cfg_attr(feature = "intrinsics", feature(core_intrinsics))]
+#![cfg_attr(feature = "trusted_len", feature(trusted_len))]
 #![cfg_attr(feature = "optimize", feature(optimize_attribute))]
 #![allow(unused_unsafe)]
 #![allow(non_camel_case_types)]