add try from methods

Cargo.toml

@@ -16,7 +16,8 @@ edition = "2018"
 [package.metadata.docs.rs]
 features = ["std", "num-bigint-std", "serde"]
 
-[dependencies]
+[dependencies.paste]
+version = "1.0"
 
 [dependencies.num-bigint]
 optional = true

build.rs

@@ -4,5 +4,14 @@ fn main() {
         println!("cargo:rustc-cfg=has_int_exp_fmt");
     }
 
+    let std = if ac.probe_sysroot_crate("std") {
+        "std"
+    } else {
+        "core"
+    };
+    if ac.probe_path(&format!("{}::convert::TryFrom", std)) {
+        autocfg::emit("has_try_from");
+    }
+
     autocfg::rerun_path("build.rs");
 }

src/from.rs

@@ -0,0 +1,84 @@
+use crate::{FromPrimitive, Ratio};
+
+#[cfg(has_try_from)]
+use crate::{approximate_float, approximate_float_unsigned};
+#[cfg(has_try_from)]
+use core::convert::TryFrom;
+
+macro_rules! impl_try_from {
+    ( $($name:ty),* => $into:ty ; $approx:ident) => {
+        $(
+        #[cfg(has_try_from)]
+        impl TryFrom<$name> for Ratio<$into> {
+                type Error = ();
+                paste::paste! {
+                    fn try_from(n: $name) -> Result<Self, ()> {
+                        <$into as FromPrimitive>::[<from_ $name>](n)
+                            .map(Ratio::from_integer)
+                            .ok_or(())
+                    }
+                }
+            }
+        )*
+
+        #[cfg(has_try_from)]
+        impl TryFrom<f32> for Ratio<$into> {
+            type Error = ();
+            fn try_from(n: f32) -> Result<Self, ()> {
+                $approx(n, 10e-20, 30).ok_or(())
+            }
+        }
+
+        #[cfg(has_try_from)]
+        impl TryFrom<f64> for Ratio<$into> {
+            type Error = ();
+            fn try_from(n: f64) -> Result<Self, ()> {
+                $approx(n, 10e-20, 30).ok_or(())
+            }
+        }
+
+    };
+}
+
+impl_try_from!(i8, u16, i16, u32, i32, u64, i64, u128, i128 => u8 ; approximate_float_unsigned);
+impl_try_from!(u8, u16, i16, u32, i32, u64, i64, u128, i128 => i8 ; approximate_float);
+
+impl_try_from!(i16, u32, i32, u64, i64, u128, i128 => u16 ; approximate_float_unsigned);
+impl_try_from!(u16, u32, i32, u64, i64, u128, i128 => i16 ; approximate_float);
+
+impl_try_from!(i32, u64, i64, u128, i128 => u32 ; approximate_float_unsigned);
+impl_try_from!(u32, u64, i64, u128, i128 => i32 ; approximate_float);
+
+impl_try_from!(i64, u128, i128 => u64 ; approximate_float_unsigned);
+impl_try_from!(u64, u128, i128 => i64 ; approximate_float);
+
+impl_try_from!(i128 => u128 ; approximate_float_unsigned);
+impl_try_from!(u128 => i128 ; approximate_float);
+
+macro_rules! impl_from {
+    ( $($name:ty),* => $into:ty) => {
+        $(
+        impl From<$name> for Ratio<$into> {
+                paste::paste! {
+                    fn from(n: $name) -> Self {
+                        <$into as FromPrimitive>::[< from_ $name>](n)
+                            .map(Ratio::from_integer)
+                            .unwrap()
+                    }
+                }
+            }
+        )*
+    };
+}
+
+impl_from!(u8, u16, u32, u64 => u128);
+impl_from!(u8, i8, u16, i16, u32, i32, u64, i64 => i128);
+
+impl_from!(u8, u16, u32 => u64);
+impl_from!(u8, i8, u16, i16, u32, i32 => i64);
+
+impl_from!(u8, u16 => u32);
+impl_from!(u8, i8, u16, i16 => i32);
+
+impl_from!(u8 => u16);
+impl_from!(u8, i8 => i16);

src/lib.rs

@@ -44,6 +44,7 @@ use num_traits::{
     Pow, Signed, Zero,
 };
 
+mod from;
 mod pow;
 
 /// Represents the ratio between two numbers.