include_data 0.1.0

# include_data - Include typed data directly in your executable

## Stability

While this crate is pre-1.0 you should consider both the API and semantics
unstable. However, this is simply to allow thorough community-review of the
soundness of implementation. I hope that a 1.0 release will come relatively
quickly with few API changes.

## Including data

Sometimes, you want to include data directly in your executable file, but
you don't want to translate that data into Rust cod that does the `static`
initialization. This is very useful in embedded contexts, or if you have
some (usually relatively small) data that will always be needed, and you
don't want to deal with loading it from the filesystem and distributing it
as a separate file.

The Rust standard library (and core library) contains
[`include_bytes`][core::include_bytes] for this purpose. This macro will
give you a static reference to a binary array containing the data from a
file: that is, a `&'static [u8; N]`.

However, if you want to use your static data, you often want it to be of a
particular type, not just a `[u8]`. For example, you may know that your
included file is a sequence of `f64`s, or a UTF-32 file, or of some
custom type. This crate provides macros for typed compile-time data
includes. This is provided by two main macros:

- [`include_data`] - outputs any type which is sound
- [`include_slice`] - outputs a `&'static [T]` slice for any `T` for which
                      this is sound

 ## Usage

 This library will work out-of-the-box with any type that implements
 [`bytemuck::Pod`]. This includes:

 - Primitive numerical types (`u16`, `i32`, `f64`, etc.)
 - Arrays of primitive numerical types (e.g. `[f32; N]`)

 For example:
 ```rust
 static MY_INTEGER: i32 = include_data!("../tests/test_data/file_exactly_4_bytes_long");
 static SOME_TEXT: &[u32] = include_slice!(u32, "../tests/test_data/some_utf-32_file");
 static FOUR_BYTES: [u8; 4] = include_data!("../tests/test_data/file_exactly_4_bytes_long");
 ```

 Aliases are provided for `include_slice` for primitive number types, using
 them is a matter of personal preference. For example:
 ```rust
 static SOME_TEXT: &[u32] = include_u32!("../tests/test_data/some_utf-32_file");
 ```

 ## Usage with custom types

 You can include data in any custom type you like. The best way of doing this
 is if your custom type satisfies the requirements for [`bytemuck::Pod`],
 in which case you can simply use [`include_data`].

 ```rust
 #[repr(C)]
 #[derive(Copy, Clone)]
 struct Foo {
     integer: u16,
     pair: (u8, u8),
 }

 // Safety: the requirements for `Pod` have been manually checked.
 unsafe impl bytemuck::Zeroable for Foo {}
 unsafe impl bytemuck::Pod for Foo {}

 static FOO_DATA: Foo = include_data!("../tests/test_data/file_exactly_4_bytes_long");
 ```

 Alternatively, if your type cannot implement `bytemuck::Pod` (especially
 if it is a foreign type over which you have no control), [`include_unsafe`]
 can be used. In this case, you must guarantee that the file included is
 valid for the target type. This may depend on host platform, compiler
 version, and compiler profile (amongst other things): recall that Rust does
 not have a stable ABI. Clearly, this is **very** unsafe and should be
 avoided if possible.

 ```rust
 #[repr(C)]
 struct StructWithPadding {
     byte: u8,
     two_bytes: u16,
 }

 // Safety: we guarantee that the included file contains bytes which are
 // a valid bit-pattern for our struct, when compiled on this host.
 static BAR_DATA: StructWithPadding = unsafe { include_unsafe!("../tests/test_data/file_exactly_4_bytes_long") };
 ```

 ## Safety

 All macros exported by this crate are safe, except [`include_unsafe`]
 (assuming, of course, that implementations of `bytemuck::Pod` are sound). If
 the input file size does not match the target type (or is not divisible by
 it, in the case of slices) or the file cannot be read, compilation will
 fail.

 [`include_unsafe`] is **very** unsafe and should be used with great care.
 See the linked documentation for full details.

 ## MSRV

 This crate is tested against a fixed version of the Rust compiler (found
 in `rust-toolchain.toml`) only so that compiler errors can be consistently
 tested. However, all features relied upon were present in Rust 1.0.

 ## Prior art

 The techniques used by this crate were published in a
 [blog post by Jack Wrenn](https://jack.wrenn.fyi/blog/include-transmute/).
 Some of those techniques were original to Jack, while others were found
 in forum threads linked from that post. Please do reach out if you are
 somebody involved with these discussions, or have any prior work in this
 area. I am also grateful to Jack for comments on an earlier draft of this
 crate.