Switch everything from lazy_static to once_cell::Lazy

Fewer macros, faster compile-time and the Lazy type will likely end up
in the standard library in a similar form to this.

examples/Cargo.toml

@@ -30,7 +30,7 @@ pango = { git = "https://github.com/gtk-rs/pango", optional = true }
 pangocairo = { git = "https://github.com/gtk-rs/pangocairo", optional = true }
 glutin = { version = "0.21", optional = true }
 winit = { version = "0.19", optional = true }
-lazy_static = "1.0"
+once_cell = "1.0"
 
 [build-dependencies]
 gl_generator = { version = "0.14", optional = true }

examples/src/bin/subclass.rs

@@ -42,16 +42,16 @@ mod fir_filter {
     extern crate byte_slice_cast;
     use byte_slice_cast::*;
 
-    use lazy_static::lazy_static;
+    use once_cell::sync::Lazy;
 
     // The debug category we use below for our filter
-    lazy_static! {
+    pub static CAT: Lazy<gst::DebugCategory> = Lazy::new(|| {
-        pub static ref CAT: gst::DebugCategory = gst::DebugCategory::new(
+        gst::DebugCategory::new(
             "rsfirfilter",
             gst::DebugColorFlags::empty(),
             Some("Rust FIR Filter"),
-        );
+        )
-    }
+    });
 
     // In the imp submodule we include the actual implementation
     mod imp {

gstreamer-gl/Cargo.toml

@@ -17,7 +17,7 @@ build = "build.rs"
 bitflags = "1.0"
 byteorder = "1"
 libc = "0.2"
-lazy_static = "1.0"
+once_cell = "1.0"
 glib-sys = { git = "https://github.com/gtk-rs/sys" }
 gobject-sys = { git = "https://github.com/gtk-rs/sys" }
 gstreamer-sys = { git = "https://gitlab.freedesktop.org/gstreamer/gstreamer-rs-sys", features = ["v1_14"] }

gstreamer-gl/src/caps_features.rs

@@ -10,12 +10,12 @@ use gst::CapsFeatures;
 use gst_gl_sys;
 use std::ffi::CStr;
 
-lazy_static! {
+use once_cell::sync::Lazy;
-    pub static ref CAPS_FEATURE_MEMORY_GL_MEMORY: &'static str = unsafe {
+
+pub static CAPS_FEATURE_MEMORY_GL_MEMORY: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_gl_sys::GST_CAPS_FEATURE_MEMORY_GL_MEMORY)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref CAPS_FEATURES_MEMORY_GL_MEMORY: CapsFeatures =
+pub static CAPS_FEATURES_MEMORY_GL_MEMORY: Lazy<CapsFeatures> =
-        CapsFeatures::new(&[*CAPS_FEATURE_MEMORY_GL_MEMORY]);
+    Lazy::new(|| CapsFeatures::new(&[*CAPS_FEATURE_MEMORY_GL_MEMORY]));
-}

gstreamer-gl/src/gl_display.rs

@@ -9,10 +9,10 @@
 use gst_gl_sys;
 use std::ffi::CStr;
 
-lazy_static! {
+use once_cell::sync::Lazy;
-    pub static ref GL_DISPLAY_CONTEXT_TYPE: &'static str = unsafe {
+
+pub static GL_DISPLAY_CONTEXT_TYPE: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_gl_sys::GST_GL_DISPLAY_CONTEXT_TYPE)
         .to_str()
         .unwrap()
-    };
+});
-}

gstreamer-gl/src/lib.rs

@@ -10,9 +10,8 @@
 #[macro_use]
 extern crate bitflags;
 extern crate byteorder;
-#[macro_use]
-extern crate lazy_static;
 extern crate libc;
+extern crate once_cell;
 #[macro_use]
 extern crate glib;
 extern crate glib_sys;

gstreamer-rtsp-server/Cargo.toml

@@ -15,7 +15,7 @@ build = "build.rs"
 [dependencies]
 bitflags = "1.0"
 libc = "0.2"
-lazy_static = "1.0"
+once_cell = "1.0"
 glib-sys = { git = "https://github.com/gtk-rs/sys" }
 gio-sys = { git = "https://github.com/gtk-rs/sys" }
 gobject-sys = { git = "https://github.com/gtk-rs/sys" }

gstreamer-rtsp-server/src/lib.rs

@@ -8,9 +8,8 @@
 
 #[macro_use]
 extern crate bitflags;
-#[macro_use]
-extern crate lazy_static;
 extern crate libc;
+extern crate once_cell;
 
 extern crate gio;
 extern crate gio_sys as gio_sys;
@@ -71,63 +70,63 @@ pub use rtsp_stream_transport::RTSPStreamTransportExtManual;
 pub use rtsp_context::*;
 pub use rtsp_token::*;
 
-lazy_static! {
+use once_cell::sync::Lazy;
-    pub static ref RTSP_ADDRESS_POOL_ANY_IPV4: &'static str = unsafe {
+
+pub static RTSP_ADDRESS_POOL_ANY_IPV4: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_ADDRESS_POOL_ANY_IPV4)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_ADDRESS_POOL_ANY_IPV6: &'static str = unsafe {
+pub static RTSP_ADDRESS_POOL_ANY_IPV6: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_ADDRESS_POOL_ANY_IPV6)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_AUTH_CHECK_CONNECT: &'static str = unsafe {
+pub static RTSP_AUTH_CHECK_CONNECT: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_AUTH_CHECK_CONNECT)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_AUTH_CHECK_MEDIA_FACTORY_ACCESS: &'static str = unsafe {
+pub static RTSP_AUTH_CHECK_MEDIA_FACTORY_ACCESS: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_AUTH_CHECK_MEDIA_FACTORY_ACCESS)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_AUTH_CHECK_MEDIA_FACTORY_CONSTRUCT: &'static str = unsafe {
+pub static RTSP_AUTH_CHECK_MEDIA_FACTORY_CONSTRUCT: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_AUTH_CHECK_MEDIA_FACTORY_CONSTRUCT)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_AUTH_CHECK_TRANSPORT_CLIENT_SETTINGS: &'static str = unsafe {
+pub static RTSP_AUTH_CHECK_TRANSPORT_CLIENT_SETTINGS: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_AUTH_CHECK_TRANSPORT_CLIENT_SETTINGS)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_AUTH_CHECK_URL: &'static str = unsafe {
+pub static RTSP_AUTH_CHECK_URL: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_AUTH_CHECK_URL)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_PERM_MEDIA_FACTORY_ACCESS: &'static str = unsafe {
+pub static RTSP_PERM_MEDIA_FACTORY_ACCESS: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_PERM_MEDIA_FACTORY_ACCESS)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_PERM_MEDIA_FACTORY_CONSTRUCT: &'static str = unsafe {
+pub static RTSP_PERM_MEDIA_FACTORY_CONSTRUCT: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_PERM_MEDIA_FACTORY_CONSTRUCT)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_TOKEN_MEDIA_FACTORY_ROLE: &'static str = unsafe {
+pub static RTSP_TOKEN_MEDIA_FACTORY_ROLE: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_TOKEN_MEDIA_FACTORY_ROLE)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref RTSP_TOKEN_TRANSPORT_CLIENT_SETTINGS: &'static str = unsafe {
+pub static RTSP_TOKEN_TRANSPORT_CLIENT_SETTINGS: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_rtsp_server_sys::GST_RTSP_TOKEN_TRANSPORT_CLIENT_SETTINGS)
         .to_str()
         .unwrap()
-    };
+});
-}
 
 // Re-export all the traits in a prelude module, so that applications
 // can always "use gst::prelude::*" without getting conflicts

gstreamer-video/Cargo.toml

@@ -23,7 +23,7 @@ gstreamer-video-sys = { git = "https://gitlab.freedesktop.org/gstreamer/gstreame
 glib = { git = "https://github.com/gtk-rs/glib" }
 gstreamer = { path = "../gstreamer" }
 gstreamer-base = { path = "../gstreamer-base" }
-lazy_static = "1.0"
+once_cell = "1.0"
 
 [build-dependencies]
 rustdoc-stripper = { version = "0.1", optional = true }

gstreamer-video/src/lib.rs

@@ -8,9 +8,8 @@
 
 #[macro_use]
 extern crate bitflags;
-#[macro_use]
-extern crate lazy_static;
 extern crate libc;
+extern crate once_cell;
 
 #[macro_use]
 extern crate glib;

gstreamer-video/src/video_buffer_pool.rs

@@ -12,28 +12,30 @@ use std::mem;
 
 use glib::translate::*;
 
-lazy_static! {
+use once_cell::sync::Lazy;
-    pub static ref BUFFER_POOL_OPTION_VIDEO_AFFINE_TRANSFORMATION_META: &'static str = unsafe {
+
+pub static BUFFER_POOL_OPTION_VIDEO_AFFINE_TRANSFORMATION_META: Lazy<&'static str> =
+    Lazy::new(|| unsafe {
         CStr::from_ptr(gst_video_sys::GST_BUFFER_POOL_OPTION_VIDEO_AFFINE_TRANSFORMATION_META)
             .to_str()
             .unwrap()
-    };
+    });
-    pub static ref BUFFER_POOL_OPTION_VIDEO_ALIGNMENT: &'static str = unsafe {
+pub static BUFFER_POOL_OPTION_VIDEO_ALIGNMENT: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_video_sys::GST_BUFFER_POOL_OPTION_VIDEO_ALIGNMENT)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref BUFFER_POOL_OPTION_VIDEO_GL_TEXTURE_UPLOAD_META: &'static str = unsafe {
+pub static BUFFER_POOL_OPTION_VIDEO_GL_TEXTURE_UPLOAD_META: Lazy<&'static str> =
+    Lazy::new(|| unsafe {
         CStr::from_ptr(gst_video_sys::GST_BUFFER_POOL_OPTION_VIDEO_GL_TEXTURE_UPLOAD_META)
             .to_str()
             .unwrap()
-    };
+    });
-    pub static ref BUFFER_POOL_OPTION_VIDEO_META: &'static str = unsafe {
+pub static BUFFER_POOL_OPTION_VIDEO_META: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_video_sys::GST_BUFFER_POOL_OPTION_VIDEO_META)
         .to_str()
         .unwrap()
-    };
+});
-}
 
 #[derive(Debug, Clone)]
 pub struct VideoAlignment(pub(crate) gst_video_sys::GstVideoAlignment);

gstreamer/Cargo.toml

@@ -21,7 +21,7 @@ gobject-sys = { git = "https://github.com/gtk-rs/sys" }
 gstreamer-sys = { git = "https://gitlab.freedesktop.org/gstreamer/gstreamer-rs-sys", features = ["v1_8"] }
 glib = { git = "https://github.com/gtk-rs/glib" }
 num-rational = { version = "0.2", default-features = false, features = [] }
-lazy_static = "1.0"
+once_cell = "1.0"
 futures-core = "0.3"
 futures-util = "0.3"
 futures-channel = "0.3"

gstreamer/src/buffer.rs

@@ -878,12 +878,10 @@ impl<T> Eq for MappedBuffer<T> {}
 unsafe impl<T> Send for MappedBuffer<T> {}
 unsafe impl<T> Sync for MappedBuffer<T> {}
 
-lazy_static! {
+pub const BUFFER_COPY_METADATA: ::BufferCopyFlags =
-    pub static ref BUFFER_COPY_METADATA: ::BufferCopyFlags =
+    ::BufferCopyFlags::from_bits_truncate(gst_sys::GST_BUFFER_COPY_METADATA);
-        ::BufferCopyFlags::FLAGS | ::BufferCopyFlags::TIMESTAMPS | ::BufferCopyFlags::META;
+pub const BUFFER_COPY_ALL: ::BufferCopyFlags =
-    pub static ref BUFFER_COPY_ALL: ::BufferCopyFlags =
+    ::BufferCopyFlags::from_bits_truncate(gst_sys::GST_BUFFER_COPY_ALL);
-        *BUFFER_COPY_METADATA | ::BufferCopyFlags::MEMORY;
-}
 
 #[cfg(test)]
 mod tests {

gstreamer/src/caps_features.rs

@@ -15,6 +15,8 @@ use std::ops::{Deref, DerefMut};
 use std::ptr;
 use std::str;
 
+use once_cell::sync::Lazy;
+
 use glib;
 use glib::translate::{
     from_glib, from_glib_full, from_glib_none, FromGlibPtrFull, FromGlibPtrNone, GlibPtrDefault,
@@ -461,15 +463,13 @@ impl ToOwned for CapsFeaturesRef {
 unsafe impl Sync for CapsFeaturesRef {}
 unsafe impl Send for CapsFeaturesRef {}
 
-lazy_static! {
+pub static CAPS_FEATURE_MEMORY_SYSTEM_MEMORY: Lazy<&'static str> = Lazy::new(|| unsafe {
-    pub static ref CAPS_FEATURE_MEMORY_SYSTEM_MEMORY: &'static str = unsafe {
     CStr::from_ptr(gst_sys::GST_CAPS_FEATURE_MEMORY_SYSTEM_MEMORY)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref CAPS_FEATURES_MEMORY_SYSTEM_MEMORY: CapsFeatures =
+pub static CAPS_FEATURES_MEMORY_SYSTEM_MEMORY: Lazy<CapsFeatures> =
-        CapsFeatures::new(&[*CAPS_FEATURE_MEMORY_SYSTEM_MEMORY]);
+    Lazy::new(|| CapsFeatures::new(&[*CAPS_FEATURE_MEMORY_SYSTEM_MEMORY]));
-}
 
 #[cfg(test)]
 mod tests {

gstreamer/src/element.rs

@@ -9,6 +9,8 @@
 use Element;
 use ElementClass;
 
+use once_cell::sync::Lazy;
+
 use glib;
 #[cfg(any(feature = "v1_10", feature = "dox"))]
 use glib::object::Cast;
@@ -845,38 +847,36 @@ impl ElementClass {
     }
 }
 
-lazy_static! {
+pub static ELEMENT_METADATA_AUTHOR: Lazy<&'static str> = Lazy::new(|| unsafe {
-    pub static ref ELEMENT_METADATA_AUTHOR: &'static str = unsafe {
     CStr::from_ptr(gst_sys::GST_ELEMENT_METADATA_AUTHOR)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref ELEMENT_METADATA_DESCRIPTION: &'static str = unsafe {
+pub static ELEMENT_METADATA_DESCRIPTION: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_sys::GST_ELEMENT_METADATA_DESCRIPTION)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref ELEMENT_METADATA_DOC_URI: &'static str = unsafe {
+pub static ELEMENT_METADATA_DOC_URI: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_sys::GST_ELEMENT_METADATA_DOC_URI)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref ELEMENT_METADATA_ICON_NAME: &'static str = unsafe {
+pub static ELEMENT_METADATA_ICON_NAME: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_sys::GST_ELEMENT_METADATA_ICON_NAME)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref ELEMENT_METADATA_KLASS: &'static str = unsafe {
+pub static ELEMENT_METADATA_KLASS: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_sys::GST_ELEMENT_METADATA_KLASS)
         .to_str()
         .unwrap()
-    };
+});
-    pub static ref ELEMENT_METADATA_LONGNAME: &'static str = unsafe {
+pub static ELEMENT_METADATA_LONGNAME: Lazy<&'static str> = Lazy::new(|| unsafe {
     CStr::from_ptr(gst_sys::GST_ELEMENT_METADATA_LONGNAME)
         .to_str()
         .unwrap()
-    };
+});
-}
 
 #[macro_export]
 macro_rules! gst_element_error(

gstreamer/src/lib.rs

@@ -12,9 +12,8 @@ extern crate bitflags;
 #[cfg(any(feature = "v1_14", feature = "dox"))]
 #[macro_use]
 extern crate cfg_if;
-#[macro_use]
-extern crate lazy_static;
 extern crate libc;
+extern crate once_cell;
 extern crate thiserror;
 
 // Re-exported for the subclass gst_plugin_define! macro

gstreamer/src/log.rs

@@ -14,6 +14,8 @@ use std::ffi::CStr;
 use std::fmt;
 use std::ptr;
 
+use once_cell::sync::Lazy;
+
 use gobject_sys;
 use gst_sys;
 
@@ -167,20 +169,18 @@ impl fmt::Debug for DebugCategory {
     }
 }
 
-lazy_static! {
+pub static CAT_RUST: Lazy<DebugCategory> = Lazy::new(|| {
-    pub static ref CAT_RUST: DebugCategory = DebugCategory::new(
+    DebugCategory::new(
         "GST_RUST",
         ::DebugColorFlags::UNDERLINE,
         Some("GStreamer's Rust binding core"),
-    );
+    )
-}
+});
 
 macro_rules! declare_debug_category_from_name(
     ($cat:ident, $cat_name:expr) => (
-        lazy_static! {
+        pub static $cat: Lazy<DebugCategory> = Lazy::new(|| DebugCategory::get($cat_name)
-            pub static ref $cat: DebugCategory = DebugCategory::get($cat_name)
+            .expect(&format!("Unable to find `DebugCategory` with name {}", $cat_name)));
-                .expect(&format!("Unable to find `DebugCategory` with name {}", $cat_name));
-        }
     );
 );
 

gstreamer/src/tags.rs

@@ -11,6 +11,8 @@ use std::fmt;
 use std::marker::PhantomData;
 use std::mem;
 
+use once_cell::sync::Lazy;
+
 use glib;
 use glib::translate::{
     from_glib, from_glib_full, FromGlibPtrFull, ToGlib, ToGlibPtr, ToGlibPtrMut,
@@ -42,10 +44,8 @@ macro_rules! impl_tag(
             }
         }
 
-        lazy_static! {
+        pub(crate) static $rust_tag: Lazy<&'static str> = Lazy::new(||
-            pub(crate) static ref $rust_tag: &'static str =
+            unsafe { CStr::from_ptr(gst_sys::$gst_tag).to_str().unwrap() });
-                unsafe { CStr::from_ptr(gst_sys::$gst_tag).to_str().unwrap() };
-        }
     };
 );
 

gstreamer/src/value_serde.rs

@@ -18,6 +18,8 @@ use serde::ser::{Serialize, SerializeTuple, Serializer};
 
 use std::{fmt, mem};
 
+use once_cell::sync::Lazy;
+
 use Buffer;
 use DateTime;
 use Sample;
@@ -32,20 +34,20 @@ fn get_other_type_id<T: StaticType>() -> usize {
     }
 }
 
-lazy_static! {
+pub(crate) static ARRAY_OTHER_TYPE_ID: Lazy<usize> = Lazy::new(get_other_type_id::<Array>);
-    pub(crate) static ref ARRAY_OTHER_TYPE_ID: usize = get_other_type_id::<Array>();
+pub(crate) static BITMASK_OTHER_TYPE_ID: Lazy<usize> = Lazy::new(get_other_type_id::<Bitmask>);
-    pub(crate) static ref BITMASK_OTHER_TYPE_ID: usize = get_other_type_id::<Bitmask>();
+pub(crate) static DATE_OTHER_TYPE_ID: Lazy<usize> = Lazy::new(get_other_type_id::<Date>);
-    pub(crate) static ref DATE_OTHER_TYPE_ID: usize = get_other_type_id::<Date>();
+pub(crate) static DATE_TIME_OTHER_TYPE_ID: Lazy<usize> = Lazy::new(get_other_type_id::<DateTime>);
-    pub(crate) static ref DATE_TIME_OTHER_TYPE_ID: usize = get_other_type_id::<DateTime>();
+pub(crate) static FRACTION_OTHER_TYPE_ID: Lazy<usize> = Lazy::new(get_other_type_id::<Fraction>);
-    pub(crate) static ref FRACTION_OTHER_TYPE_ID: usize = get_other_type_id::<Fraction>();
+pub(crate) static FRACTION_RANGE_OTHER_TYPE_ID: Lazy<usize> =
-    pub(crate) static ref FRACTION_RANGE_OTHER_TYPE_ID: usize =
+    Lazy::new(get_other_type_id::<FractionRange>);
-        get_other_type_id::<FractionRange>();
+pub(crate) static INT_RANGE_I32_OTHER_TYPE_ID: Lazy<usize> =
-    pub(crate) static ref INT_RANGE_I32_OTHER_TYPE_ID: usize = get_other_type_id::<IntRange<i32>>();
+    Lazy::new(get_other_type_id::<IntRange<i32>>);
-    pub(crate) static ref INT_RANGE_I64_OTHER_TYPE_ID: usize = get_other_type_id::<IntRange<i64>>();
+pub(crate) static INT_RANGE_I64_OTHER_TYPE_ID: Lazy<usize> =
-    pub(crate) static ref LIST_OTHER_TYPE_ID: usize = get_other_type_id::<List>();
+    Lazy::new(get_other_type_id::<IntRange<i64>>);
-    pub(crate) static ref SAMPLE_OTHER_TYPE_ID: usize = get_other_type_id::<Sample>();
+pub(crate) static LIST_OTHER_TYPE_ID: Lazy<usize> = Lazy::new(get_other_type_id::<List>);
-    pub(crate) static ref BUFFER_OTHER_TYPE_ID: usize = get_other_type_id::<Buffer>();
+pub(crate) static SAMPLE_OTHER_TYPE_ID: Lazy<usize> = Lazy::new(get_other_type_id::<Sample>);
-}
+pub(crate) static BUFFER_OTHER_TYPE_ID: Lazy<usize> = Lazy::new(get_other_type_id::<Buffer>);
 
 impl<'a> Serialize for Fraction {
     fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {