impl const From<num> for num

Author: usbalbin

library/core/src/convert/num.rs

@@ -45,7 +45,8 @@ impl_float_to_int!(f64 => u8 u16 u32 u64 u128 usize i8 i16 i32 i64 i128 isize);
 macro_rules! impl_from {
     ($Small: ty, $Large: ty, #[$attr:meta], $doc: expr) => {
         #[$attr]
-        impl From<$Small> for $Large {
+        #[rustc_const_unstable(feature = "const_num_from_num", issue = "87852")]
+        impl const From<$Small> for $Large {
             // Rustdocs on the impl block show a "[+] show undocumented items" toggle.
             // Rustdocs on functions do not.
             #[doc = $doc]
@@ -172,7 +173,8 @@ impl_from! { f32, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0"
 macro_rules! try_from_unbounded {
     ($source:ty, $($target:ty),*) => {$(
         #[stable(feature = "try_from", since = "1.34.0")]
-        impl TryFrom<$source> for $target {
+        #[rustc_const_unstable(feature = "const_num_from_num", issue = "87852")]
+        impl const TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
             /// Try to create the target number type from a source
@@ -190,7 +192,8 @@ macro_rules! try_from_unbounded {
 macro_rules! try_from_lower_bounded {
     ($source:ty, $($target:ty),*) => {$(
         #[stable(feature = "try_from", since = "1.34.0")]
-        impl TryFrom<$source> for $target {
+        #[rustc_const_unstable(feature = "const_num_from_num", issue = "87852")]
+        impl const TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
             /// Try to create the target number type from a source
@@ -212,7 +215,8 @@ macro_rules! try_from_lower_bounded {
 macro_rules! try_from_upper_bounded {
     ($source:ty, $($target:ty),*) => {$(
         #[stable(feature = "try_from", since = "1.34.0")]
-        impl TryFrom<$source> for $target {
+        #[rustc_const_unstable(feature = "const_num_from_num", issue = "87852")]
+        impl const TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
             /// Try to create the target number type from a source
@@ -234,7 +238,8 @@ macro_rules! try_from_upper_bounded {
 macro_rules! try_from_both_bounded {
     ($source:ty, $($target:ty),*) => {$(
         #[stable(feature = "try_from", since = "1.34.0")]
-        impl TryFrom<$source> for $target {
+        #[rustc_const_unstable(feature = "const_num_from_num", issue = "87852")]
+        impl const TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
             /// Try to create the target number type from a source

library/core/src/lib.rs

@@ -99,6 +99,7 @@
 #![feature(const_slice_from_raw_parts)]
 #![feature(const_slice_ptr_len)]
 #![feature(const_swap)]
+#![feature(const_trait_impl)]
 #![feature(const_type_id)]
 #![feature(const_type_name)]
 #![feature(const_unreachable_unchecked)]