:tada: first trait Float

.gitignore

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+# Rust
+/target
+/Cargo.lock
+
+# CLion/IDEA
+*.iml
+.idea/*
+!.idea/codeStyles/
+
+# MacOS
+.DS_Store

Cargo.toml

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+[package]
+name = "lineal"
+authors = ["Felix Bytow <drako@drako.guru>"]
+version = "0.1.0"
+edition = "2021"
+publish = ["crates-drako-guru"]
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/lib.rs

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+pub use self::traits::Float;
+
+mod traits;

src/traits/float.rs

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+/// Marker trait because certain operations only make sense on floating point types.
+pub trait Float {}
+
+impl Float for f32 {}
+
+impl Float for f64 {}
+
+#[cfg(test)]
+mod tests {
+    use crate::Float;
+
+    fn is_float<T: Float>() -> bool {
+        true
+    }
+
+    #[test]
+    fn f32_is_a_float() {
+        assert!(is_float::<f64>());
+    }
+
+    #[test]
+    fn f64_is_a_float() {
+        assert!(is_float::<f64>());
+    }
+}

src/traits/mod.rs

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+pub use self::float::Float;
+
+mod float;