Make the crate no_std-compliant, add "std" feature

Author: aldanor

Cargo.toml

@@ -5,14 +5,18 @@ authors = ["Ivan Smirnov <i.s.smirnov@gmail.com>"]
 repository = "https://github.com/aldanor/fast-float-rust"
 documentation = "https://docs.rs/fast-float"
 description = "Fast floating-point number parser."
-keywords = ["parser", "parsing", "parse", "float"]
-categories = ["parser-implementations", "parsing", "text-processing", "algorithms"]
+keywords = ["parser", "parsing", "parse", "float", "no-std"]
+categories = ["parser-implementations", "parsing", "text-processing", "algorithms", "no-std"]
 readme = "README.md"
 license = "MIT OR Apache-2.0"
 autobenches = false
 edition = "2018"
 exclude = ["benches/*", "extras/*"]
 
+[features]
+default = ["std"]
+std = []
+
 [dev-dependencies]
 lexical-core = "0.7"
 criterion = "0.3"
@@ -37,3 +41,6 @@ members = [".", "extras/data-tests", "extras/simple-bench"]
 [profile.release]
 lto = "fat"
 codegen-units = 1
+
+[package.metadata.docs.rs]
+features = ["std"]

src/common.rs

@@ -1,5 +1,5 @@
-use std::marker::PhantomData;
-use std::ptr;
+use core::marker::PhantomData;
+use core::ptr;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct AsciiStr<'a> {

src/float.rs

@@ -1,5 +1,5 @@
-use std::fmt::{Debug, Display};
-use std::ops::{Add, Div, Mul, Neg};
+use core::fmt::{Debug, Display};
+use core::ops::{Add, Div, Mul, Neg};
 
 mod private {
     pub trait Sealed {}

src/lib.rs

@@ -11,8 +11,7 @@
     clippy::cargo_common_metadata
 )]
 
-use std::error::Error as StdError;
-use std::fmt::{self, Display};
+use core::fmt::{self, Display};
 
 mod binary;
 mod common;
@@ -32,10 +31,15 @@ impl Display for Error {
     }
 }
 
-impl StdError for Error {}
+#[cfg(feature = "std")]
+impl std::error::Error for Error {
+    fn description(&self) -> &str {
+        "error while parsing a float"
+    }
+}
 
 /// Result type alias for fast-float parsing functions.
-pub type Result<T> = std::result::Result<T, Error>;
+pub type Result<T> = core::result::Result<T, Error>;
 
 /// Trait for numerical float types that can be parsed from string.
 pub trait FastFloat: float::Float {

src/parse.rs

@@ -1,4 +1,4 @@
-use std::mem;
+use core::mem;
 
 use crate::binary::compute_float;
 use crate::float::Float;